Wireless powering and communication system for communicating data between a host system and a stand-alone device

ABSTRACT

A wireless communication system for communicating between a host system and a stand-alone device through an electromagnetic coupling medium is disclosed. The communication system has the capabilities of bi-directional data communications between the host and the stand-alone device and of powering the stand-alone device with energy pulses coupled through the electromagnetic coupling medium from the host. The electromagnetic medium is capable of supporting the bi-directional flow of energy pulses and energy transitions thereof between the host and stand-alone device. In one embodiment, bi-directional communication is provided by transmitting and detecting predetermined numbers of consecutive energy transitions coupled through the medium. Resting durations immediately precede and follow each predetermined number of consecutive energy transitions. In a preferred embodiment of the present invention, the host communicates a first binary value to the stand-alone device by coupling a first predetermined number of consecutive energy transitions to the device and a second binary value to the device by coupling a second predetermined number of consecutive energy transitions. Additionally, the host system receives data from the stand-alone device by first coupling a third predetermined number of consecutive energy transitions to the stand-alone device. The stand-alone device then responds by coupling a predetermined number of energy transitions to the medium during the resting duration following the host&#39;s transmission of the third predetermined number of consecutive energy transitions. The number of energy transitions sent by the stand-alone device during this resting duration is related to the value of the data digit being sent to the host.

This is a divisional of application Ser. No. 07/974,131 filed Nov. 10,1992, now U.S. Pat. No. 5,434,396.

The present invention relates to communication systems, and methods andapparatus thereof, for communicating between a host system and astand-alone device, such as an integrated circuit device, through anelectromagnetic medium and for providing the capability ofsimultaneously powering the stand-alone device with energy coupledthrough the medium. In particular, the present invention relates tosingle-chip communication systems, methods and apparatus thereof, forcommunicating between a host and a stand-alone integrated circuit deviceand for simultaneously powering the integrated circuit.

BACKGROUND OF THE INVENTION

Various means and methods for communicating between a stand-alone deviceand a host environment without the need for direct wire connections arecurrently known in the art. An example of such stand-alone devices areintegrated-circuit storage devices, usually of the non-volatile type,which may store business transaction information, such as credit cardinformation. An example of a host environment which would operate withsuch a credit card would be an electronic information processing devicewhich utilizes and updates the information stored by the above-mentionedintegrated-circuit storage devices. Another example of such astand-alone device would be a security pass card which, upon beingpowered, would output a digital "password" to a corresponding hostenvironment for security clearance. The advantage of these wirelesssystems over conventional magnetic-strip information bearing cards andthe like is that they provide a more reliable communications channelbetween the host and the stand-alone device (e.g., card) because theyare "contactless" systems. However, these wireless systems are moreexpensive to manufacture and have different reliability problems, asdiscussed below in grater detail.

Such prior art "wireless" stand-alone devices are generally constructedwith a plurality of I.C. chips and magnetic coil components disposed ona substrate carrier (e.g., "credit card") using hybrid circuitconstruction techniques. This is because relatively complicatedcommunications techniques are used by these wireless devices, whichrequire multiple coils and multiple processing chips. For example, U.S.Pat. No. 4,605,844 to Haggan teaches a hybrid construction of twointegrated circuit chips, three magnetic coils, and three separatecommunication channels for power, incoming data, and outgoing data in astand-alone device. U.S. Pat. No. 4,720,626 to Nishikawa, et al.,teaches a hybrid construction for a stand-alone device including an I.C.chip, a first coil for clock and power, a second coil for outputtingdata, and a hall-effect device for receiving data. As with Haggan, threeseparate "channels" are used: power/clock, data in, and data out. U.S.Pat. No. 4,791,285 to Ohki also teaches a hybrid construction includingan I.C. chip and four coils (power, data in, data out, mode command).

Examples of wireless stand-alone devices using a single coil areprovided by U.S. Pat. Nos. 4,388,524 and 4,473,825, both issued toWalton. In each example, power is periodically coupled to the coil inthe stand-alone device from the host system. In each, code sequences canbe communicated by the stand-alone device to the host system using thesame coil. In the '524 patent, a variable resonant frequency circuit isformed with the coil and a variable capacitor. The resonance frequencyis modified according to the code sequence and is detected by the hostsystem. In the '825 patent, signals of difference frequencies areselectively applied to the coil according to the code sequence anddetected by the host system. The patents do not disclose the capabilityof communicating data in the reverse direction from the host system tothe stand-alone device. In these examples, the time required fortransmitting the code sequence is much greater than the time allocatedfor receiving power. This naturally requires a significant energystorage capacity in the stand-alone device. As stated in the '825patent, an electrolytic capacitor or storage battery is used to storeenergy provided by the power pulses, thus indicating a hybridconstruction. The need for such a large power storage capacity teachesaway from the formation of these systems on an integrated circuit (IC)chip (i.e., a substrate having dimensions on the order of one centimeterper chip side and less), as is done in the present invention. This isbecause present day IC chips can only provide a limited amount ofcapacitive power storage capability on the order of a few hundredpicofarads, which is several orders of magnitude less than the storagecapability of electrolytic capacitors and storage batteries.

Additionally, the physical size of the coils taught in the '524 and '825patents are relatively large and are configured as antennas disposed oncredit-card size cards (i.e., 5.5 cm by 8.5 cm). In view of the need ofthese circuits to obtain a large mount of power in a relatively shorttime duration and based on a realistic estimate of the power coupling tothe coil antennas used in these patents, it would appear to one ofordinary skill in the art that the size of these coils is on the orderof a credit card (5.5 cm by 8.5 cm). The need for large coil antennasalso teaches away from the formation of these systems on an integratedcircuit (IC) chip, as is done in the present invention. This is becausethe area that the largest present day IC chip can provide for such acoil antenna is roughly 1/45th of the area provided by a credit card. Incontrast to the circuitry of these patents, the present inventionprovides a communication means which is more power efficient than thoseused by these patents and enables the present invention to be integratedon an IC chip.

On a related point, these examples have relatively complex circuitry inthe host environment due to the use of frequency modulationtransmission. This tends to raise the cost of manufacturing thecircuitry for the host.

The cost of such hybrid construction for these wireless communicationsystems is presently too high for the credit-card and identificationmarkets to bear. Additionally, such hybrid systems may be renderedinoperative by the user flexing the carrier substrate ("credit cards),thus breaking the hybrid connectors between the components. Given thehigh volume of credit cards, security pass cards, and the like, andgiven the better communication interface of such wireless systems, thereis a great need to decrease the cost of such wireless credit cardcarriers and to correspondingly increase their durability. The presentinvention is directed towards these goals.

An example of an integrated circuit chip communication system which isdirected towards addressing the disadvantages of hybrid construction isdescribed in the monographs by Adam C. Malamy, "A Magnetic Power andCommunications Interface for Pinless Integrated Circuits", MassachusettsInstitute of Technology, September 1987, and by Charles W. Selvidge, "AMagnetic Communication Scheme for Integrated Circuits", MassachusettsInstitute of Technology, June 1987. These monographs describe a systemin which two coils are integrated on a single IC chip, a first coil forreceiving a combined power and clock signal from a first electromagneticcoupling medium and a second coil for receiving and transmitting data toand from a second separate electromagnetic coupling medium. Tocommunicate information from the host to the IC chip, the host couplesan amplitude modulation signal to the second coil. To communicateinformation from the IC chip to the host, the IC chip selectively shortsits second coil to magnetically load a corresponding coil in the host.This changes the inductance of the host's coil, which may be detected.An on-chip power supply is generated from the first coil. An on-chippower supply of ˜3 VDC at 0.9 mW was achieved (0.3 mA). Unfortunately,this level of power is not sufficient for most applications of ICwireless communication applications. In this regard, the monographs donot appear to suggest deriving power from the amplitude-modulated signalcoupled to the second coil. From their results, however, it would notappear that deriving power from the second coil would be fruitful due tothe ON/OFF amplitude modulation of the signal and the low level of powerderived from the first coil.

In contrast to the present invention, other prior art wirelesscommunications systems use a finely tuned resonant L-C circuit in thestand-alone device to increase the amount of power that can be coupledto the stand-alone device. In these systems, energy is received by thetuned L-C circuit much more efficiently at or near the L-C resonancefrequency. The frequency of the power signal from the host or masterstation must be tightly controlled to be within a narrow range offrequencies about the resonant frequency. To communicate datainformation along with the resonant power signal, these prior artsystems generally employ frequency modulation of the master station'spower signal about this narrow frequency range. These systems do notemploy selective gating of electromagnetic energy pulses in the masterstation's power signal as such gating would cause the frequency of themaster's power signal to significantly deviate from its narrow frequencyrange. This, in turn, would significantly interrupt both thecommunication of data to the stand-alone device and the coupling ofpower to the stand-alone device. In this sense, as will become apparentin view of the present invention, these prior art systems teach againstthe communication system according to the present invention.

SUMMARY OF THE INVENTION

The present invention solves the above described problems of cost andreliability of prior devices by means of a novel communication systemand associated protocol. Specifically, the present invention recognizesthat the communications between the host, hereinafter referred to as themaster station, and the stand-alone device, hereinafter referred to asthe slave station, may be accomplished with the communication of energytransitions through an electromagnetic coupling medium coupled betweenthe master and slave stations. In particular, bi-directionalcommunications can be provided by transmitting and detectingpredetermined numbers of consecutive energy transitions coupled throughthe medium, with resting durations immediately preceding and following apredetermined number of consecutive energy transitions. Additionally,the present invention further recognizes that data may be communicatedfrom the master to the slave by varying the number of consecutive energytransitions in relation to the value of the data digits being sent. Thepresent invention also recognizes that data may be communicated from theslave to the master by coupling energy transitions to the medium duringpredetermined resting durations provided by the master station. Thepresent invention further recognizes that the pulsed energy transitionsmay also be used to power the slave station (stand-alone device).Additionally, the present invention recognizes that the communicationsystem of the present invention enables both data communications andpower to be coupled through a single electromagnetic coupling medium,thus allowing the stand-alone device (slave station) to be integratedonto a single integrated circuit chip.

Broadly stated, the present invention encompasses a system for datatransmission between a master station and a slave station in which anelectromagnetic coupling medium is formed between the master station andthe slave station. The electromagnetic coupling medium is capable ofcommunicating data bi-directionally between the master station and theslave station in the form of electromagnetic energy transitions. In oneembodiment according to the present invention, the slave stationcomprises an inductor means magnetically coupled to the coupling mediumand including a segment of conductive material disposed on a substrate,preferably of an integrated-circuit chip. The inductor means includes afirst terminal and a second terminal coupled at respective ends of thesegment of conductive material. The inductor means is for receivingmagnetic energy transitions from the medium and for providing at itsterminals an electrical signal indicative of these transitions. Theslave station further comprises means coupled to the inductor means forpowering the slave station from the energy pulses coupled to it by themaster station through said energy coupling medium and a communicationmeans for selectively coupling at least one energy transition to saidelectromagnetic coupling medium in a selected time interval. Theselective coupling of transitions communicates data information to themaster station from the slave station. Additionally, in a preferredembodiment of the present invention, the selected time interval followsa consecutive number of energy transitions provided to the couplingmedium by the master station. These means enable a power efficientimplementation thereof, which enable the slave station to be integratedon a single integrated circuit chip at a significantly lower cost thatpresent day hybrid communication systems.

For communicating data from the master station to the slave station, asecond embodiment according to the present invention comprises means inthe master station for transmitting a first digital value to the slavestation, including means for causing a first predetermined number ofenergy transitions to be coupled to the medium followed by a firstresting duration in which substantially no energy transitions arecoupled to the medium by the master station. This embodiment furthercomprises means in the master station for transmitting a second digitalvalue to the slave station, including means for causing a secondpredetermined number of energy transitions to be coupled to the mediumfollowed by a second resting duration in which substantially no energytransitions are coupled to said medium by said master station. Thisembodiment further comprises means in the slave station for detectingfrom the medium the first predetermined number of energy transitionsfollowed by the first resting duration and for outputting a signalrepresentative of the first digital value in response thereto, and fordetecting the second predetermined number of energy transitions followedby the second resting duration and for outputting a signalrepresentative of the second digital value in response thereto.

For communicating data from the slave station to the master station, athird embodiment according to the present invention comprises means inthe master station for initiating a read operation from the slavestation, including means for causing a third predetermined number ofenergy transitions to be coupled to the medium followed by a thirdresting duration in which substantially no energy transitions arecoupled to the medium by the master station. This second embodimentfurther comprises means in the slave station for detecting from themedium the third predetermined number of energy transitions followed bythe third resting duration and for outputting a read command signal inresponse thereto. This embodiment further comprises means in the slavestation responsive to the read command signal for transmitting a binaryzero value to the master station, including means for causing a fourthpredetermined number of energy transitions to be coupled to the mediumby the slave station during the third resting duration. This embodimentfurther comprises means in the slave station responsive to the readcommand signal for transmitting a binary one value to the masterstation, including means for causing a fifth predetermined number ofenergy transitions to be coupled to the medium by the slave stationduring the third resting duration, the fifth predetermined number beingdifferent from the fourth predetermined number. This second embodimentfurther comprises means in the master station for detecting from themedium the fourth predetermined number of energy transitions during thethird resting duration and for outputting a signal representative of thebinary zero value in response thereto, and means in the master stationfor detecting from the medium the fifth predetermined number of energytransitions during the third resting duration and for outputting asignal representative of the binary one value in response thereto. In afurther, the slave station couples no energy transitions to the couplingmedium when sending a binary zero to the slave station and couples oneor more energy transitions to the coupling medium when sending a binaryone.

It may be appreciated that the features of either of the above first andthird embodiments of the present invention may be combined with thefeatures of the above second embodiment of the present invention toprovide a system for bi-directional communications between the masterand slave stations. It may be further appreciated that some, if not all,of these resting durations may be of substantially equal duration.

Accordingly, it is an object of the present invention to enable awireless communication receiver and transmitter system to be constructedin a single integrated circuit chip, thereby decreasing the constructioncost of devices employing the present invention.

It is another object of the present invention to provide agenerally-applicable wireless communication system which may beimplemented using a single electromagnetic communication channel (e.g.,a single magnetic path) and a minimum of one coil in the slave station.

It is a further object of the present invention to eliminate the needfor hybrid construction of the slave station, and thereby increase thedurability of credit cards and the like employing the present invention.

It is still another object of the present invention to enable theconstruction of the slave station on an integrated circuit chip havingdimensions of one centimeter per chip side and less.

It is yet another object of the present invention to provide a simpleprotocol for enabling data to be communicated as a signal modulated onthe same signal that provides power to the slave station.

These and other objects of the present invention will become apparent tothose skilled in the an from the following detailed description of theinvention and from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communications system accordingto the present invention;

FIG. 2A is a timing diagram showing the energy transitions coupledbetween the master and slave stations according to the present inventionwhere a first digital value is communicated from the master station tothe slave station;

FIG. 2B is a timing diagram showing the energy transitions coupledbetween the master and slave stations according to the present inventionwhere a second digital value is communicated from the master station tothe slave station;

FIG. 2C is a timing diagram showing the energy transitions coupledbetween the master and slave stations according to the present inventionwhere digital values are communicated from the slave station to themaster station;

FIG. 2D is a timing diagram showing the energy transitions coupledbetween the master and slave stations according to the present inventionwhere a read command is communicated from the master station to theslave station;

FIG. 2E is a timing diagram showing the energy transitions coupledbetween the master and slave stations according to the present inventionwhere a write command is communicated from the master station to theslave station;

FIG. 3 is a diagrammatic plan view/schematic isometric view of acommunication system, including a master station and a slave station,according to the present invention;

FIGS. 4A and 4B show a more detailed partial block and schematic diagramof the communication system of FIG. 3 according to the presentinvention;

FIG. 4C shows a partial block and schematic diagram of an alternateembodiment of the slave station according to the present invention;

FIG. 5A shows an exemplary embodiment of the detector means of the slavestation according to the present invention;

FIG. 5B shows waveforms for key signals of the exemplary detector meansaccording to the present invention shown in FIG. 5A;

FIG. 6 shows a timing diagram for the generation of energy pulses andtransitions by a preferred embodiment of the master station according tothe present invention;

FIG. 7 shows a flow diagram of the operation of an exemplary controlmeans for the master station according to the present invention;

FIG. 8 shows a flow diagram of the control means for the master stationaccording to the present invention coupling a selected number of energytransitions to the coupling medium;

FIGS. 9A and 9B show a flow diagram of a read-byte operation performedby the control means for the master station according to the presentinvention;

FIGS. 10A and 10B show a flow diagram of a write-byte operationperformed by the control means for the master station according to thepresent invention;

FIG. 11 shows a flow diagram of the operation of an exemplary controlmeans for the slave station according to the present invention;

FIG. 12 shows a flow diagram of the control means for the slave stationaccording to the present invention issuing a response to the masterstation;

FIGS. 13A and 13B show a flow diagram of a send-byte operation performedby the control means for the slave station according to the presentinvention;

FIGS. 14A and 14B show a flow diagram of a receive-byte operationperformed by the control means for the slave station according to thepresent invention;

FIGS. 15A and 15B show alternate embodiments of power transmittinginductor means and data receiving inductor means according to thepresent invention;

FIG. 16A is a partial schematic isometric view of a slave stationaccording to the present invention showing two inductor means accordingto the present invention disposed separately from one another; and

FIG. 16B is a partial schematic isometric view of a slave stationaccording to the present invention showing two inductor means accordingto the present invention disposed concentric to one another.

DETAILED DESCRIPTION OF THE INVENTION

A wireless communication system according to the present invention isshown at 10 in FIG. 1. Wireless communication system 10 comprises a hostsystem or master station 30, a stand-alone device or slave station 20and an electromagnetic coupling medium 11 formed between master station30 and slave station 20. Electromagnetic coupling medium 11 is capableof supporting energy conveyed from master station 30 to slave station20, and is capable of supporting energy conveyed from slave station 20to master 30. Preferably, the energy is conveyed between master station30 and slave station 20 is in the form of electromagnetic energy pulsesand energy transitions, as explained in greater detail below. In apreferred embodiment of the present invention, the electromagneticenergy is conveyed substantially through magnetic field lines, i.e.,through magnetomotive force energy.

In the preferred embodiments of the present invention, theelectromagnetic energy is conveyed through medium 11 in the form ofenergy pulses. Such an electromagnetic energy pulse begins at a firstenergy level, rises to a second energy level, stays at the second energylevel for a predetermined time duration, returns back to the firstenergy level, and stays at the first energy level for a secondpredetermined time duration. In one embodiment of the present invention,the first energy level has a value of substantially zero Joules and thesecond energy level has a non-zero value. In the change from the firstenergy level to the second energy level, an energy transition occurs.Additionally, in the change from the second energy level to the firstenergy level, another energy transition occurs.

An electromagnetic energy pulse is capable of traveling from masterstation 30 to slave station 20 and of traveling from slave station 20 tomaster station 30. As is known in the art, such electromagnetic energypulses travel at a speed approximating the speed of light. According tothe present invention the distance between stations 20 and 30 isgenerally less than a centimeter, and preferably on the order of amillimeter or less. Consequently, the electromagnetic energy pulses arereceived substantially instantaneously by each of stations 20 and 30from its respective other station.

Electromagnetic energy pulses and the corresponding energy transitionsbetween energy levels may be coupled to coupling medium 11 in aconventional manner by means provided in master station 30 or by meansin slave station 20. Such means are discussed below in greater detailwith reference to preferred master station and slave stationembodiments. Preferably, stations 20 and 30 do not coupleelectromagnetic energy pulses and transitions to medium 11 at the sametime. This is not a necessary requirement, but rather simplifies thecommunications between stations 20 and 30. It should be understood thatelectromagnetic coupling medium 11 is capable of conveying energy pulsesand energy transitions bi-directionally between stations 20 and 30. Asdiscussed below in greater detail, this capability is utilized accordingto the present invention to enable bi-directional communications betweenstations 20 and 30 and to enable the powering of slave station 20 fromenergy coupled to medium 11 by master station 30.

In a preferred embodiment of the present invention, the electromagneticenergy pulses are generated and coupled to medium 11 by the applicationof sinusoidal voltage waveforms, or cycles, to magnetic coils (e.g.,inductors) present within each of the master and slave stations. In apreferred embodiment of master station 30, a voltage cycle begins atzero volts, rises (or falls) to a first voltage level, then falls (orrises) to a second voltage level, and returns back to a value of zero.One of the voltage levels is positive and the other is negative. One ormore voltage cycles are applied to the magnetic coil consecutively in agroup to communicate information. Resting durations of substantiallyzero volts before and after the group are used to delineate the group.

A sinusoidal voltage waveform applied to the magnetic coil generates acorresponding sinusoidal magnetic field in medium 11. In turn, thesinusoidal magnetic field conveys electromagnetic energy in aquasi-sinusoidal form. This is explained as follows with reference toFIG. 6, which shows a timing diagram 500 of exemplary sinusoidal voltagecycles, current cycles, and electromagnetic cycles generated by a coilin an exemplary embodiment of master station 30. Six (6) exemplarysinusoidal voltage cycles are shown at a graph 501 in FIG. 6. Thevoltage cycles are substantially sinusoidal (i.e., of the mathematicalform sin wt) and occur sequentially after one another. There is aninitial transient response due to the finite resistances in the magneticcoil and in the circuit driving the coil. The magnitude of the transientresponse depends upon the parameter values of the magnetic coil and thevoltage source, and is preferably small.

Each voltage cycle causes a corresponding current cycle to flow in themagnetic coil, as governed by the well known differential equation V_(L)=L*dl_(L) /dt, where V_(L) is the instantaneous voltage across themagnetic coil, L is the inductor inductance, and I_(L) is theinstantaneous current in the magnetic coil. The corresponding currentcycles are shown at a graph 502 in FIG. 6. Each current cycle has aperiod on the order of the period of the corresponding voltage cycle.The start of each current cycle is delayed in time from itscorresponding voltage cycle by a phase shift determined by the values ofL, C, and R. The delay is shown at 511 in FIG. 6. Each current cycle issubstantially of a cosine form, i.e., of the mathematical form cos wt.

The current cycles flowing in the magnetic coil produce anelectromagnetic energy field in medium 11 immediately surrounding themagnetic coil. The electromagnetic field may be readily detected by asensing coil located in slave station 20. The total electromagneticenergy generated by the current flowing in the inductor is specified bythe well known relationship E=1/2L*I_(L) ². Due to the squarerelationship, each current cycle generates two energy pulses. For thecurrent cycles shown at graph 502, the corresponding energy pulses areshown at a graph 503 in FIG. 6. Each energy pulse begins at a firstenergy level of substantially zero Joules, rises to a second energylevel (where the slope in the energy equals zero), and then returns tothe first energy level of substantially zero Joules. In the change fromthe first energy level to the second energy level, an energy transitionoccurs; and in the change from the second energy level to the firstenergy level, another energy transition occurs. The shape of the laterenergy pulses is substantially of a cosine form, being of themathematical form: 1/2*(1-cos (2 wt))=(cos wt)².

In a preferred embodiment of the present invention, a partial voltagecycle is generated at the end of the sequence of voltage cycles so as tocomplete the last current cycle and the last energy pulse. The partialvoltage cycle is shown at 515 in FIG. 6. This enables the current in themagnetic coil to settle to zero amperes before the sequence of voltagecycles is terminated. As is known in the art, shutting off the voltageacross an inductor before the current in the inductor reaches zeroamperes will likely result in "ringing" caused by the inductor currentresonating with the parasitic capacitance of the inductor and of theexternal circuit. Such ringing in the master station according to thepresent invention is generally undesirable as it may generate anunpredictable number of energy pulses in medium 11. The partial voltagecycle generated at the end of the sequence of voltage cycles, asdescribed above, substantially lessens the amount of ringing by bringingthe inductor current to near zero amperes at the end the voltage cyclesequence.

In a preferred embodiment of the present invention, the numbers ofenergy pulses and energy transitions in a voltage cycle sequence arerelated to the number of voltage cycles in the sequence by the followingrelationships. First, the number of energy pulses N_(EP) is equal totwice the number of voltage cycles N_(VC) :N_(EP) =2*N_(VC). This isbecause the energy is related to the square of the current. As indicatedabove, there are two energy transitions per energy pulse. Thus, thenumber of energy transitions N_(ET) per voltage cycle sequence is equalto four times the number of voltage cycles: N_(ET) =4*N_(VC).

In a preferred embodiment of the present invention, the electromagneticenergy pulses and transitions coupled to medium 11 are detected by slavestation 20 by way of a magnetic sensing coil. As is known in the art,each electromagnetic energy pulse has corresponding changes in themagnetic flux. These changes in the magnetic flux may be detected by amagnetic coil in the slave station. A voltage is generated across theslave's magnetic coil as a function of the change in the magnetic fluxand as governed by Faraday's induction law: V∝dφ/dt. This shape of thesensed voltage is similar to the shape of the voltage across themagnetic coil in the master station. For the sequence of voltage cyclesshown in graph 501, the corresponding sensed voltage V_(S) in anexemplary embodiment of slave station 20 shown at 504 in FIG. 6. Slavestation 20 may determine the number of energy pulses coupled to it(through medium 11) in a voltage cycle sequence by counting the numberof sensed voltage cycles. One ready way of detecting the number ofcycles in the sensed voltage is to count the number of zero crossings.Such zero crossing counting is discussed in greater detail below withreference to an exemplary embodiment of slave station 20. In this way,the number of energy pulses and energy transitions coupled to medium 11by master station 30 may be detected by slave station 20. It may beappreciated that other means within slave station 20 may be used todetect the coupled energy pulses and transitions, such as hall effectdevices.

The above exemplary voltage cycles, current cycles, and energy pulsesshown in graphs 501-504 are provided with the assumption that themagnetic coils are nearly ideal (i.e., small core losses and smallparasitic capacitances and resistances), and that the detection coil ofthe slave unit does not substantially load the magnetic energy in medium11. The latter assumption is generally a valid assumption because theamount of energy coupled by slave station 20 from medium 11 is a smallpercentage of the energy provided to medium 11 by master station 30. Inpractice, each of the magnetic coils has parasitic resistance,capacitance, core loss, and a finite separation spacing distance (e.g.,air gap) from the other coil which makes the coils less than ideal.However, it is believed by the inventors that any such non-idealcharacteristics in these coils would not significantly impact therelationships between the above-described voltage cycles, currentcycles, energy pulses, and sensed voltage cycles or significantly changethe qualitative shape of these cycles and pulses.

For the case of slave station 20 coupling energy pulses and transitionsto medium 11 for reception by master station 30, the above discussionapplies with the roles of stations 20 and 30 being reversed.

Communications according to the present invention between master station30 and slave station 20 via the use of electromagnetic energytransitions is now described. Bi-directional communication is providedby transmitting and detecting predetermined numbers of consecutiveenergy transitions coupled through coupling medium 11. In a preferredembodiment of the present invention, resting durations immediatelyprecede and follow each such predetermined number of consecutive energytransitions. Such a predetermined number of consecutive energytransitions may represent a data digit or a control instruction. Such acontrol instruction may be required to support a specific communicationprotocol between master station 30 and slave station 20. Exemplarycontrol instructions would be those governing the flow and direction ofdata between stations 20 and 30, such as by master station 30instructing slave station 20 to transmit data in its buffer to masterstation 30. Further examples of control instructions are provided belowin greater detail. The data digit flowing between stations 20 and 30 maybe communicated in the form of binary digits, each binary digit havingeither a binary zero value or a binary one value. In the presentinvention, the data digit may also be communicated in other numericalbasis, such as base 4 and base 10. With base 4, for example, a datadigit would have one of four digital values at a given time.

In a preferred embodiment of the present invention, master station 30communicates data digits to slave station 20 through sets of consecutiveenergy transitions. Specifically, master station 30 includes means forcommunicating a data digit having a first digital value to slave station20. This includes means for causing a first predetermined number ofconsecutive energy transitions to be coupled to medium 11, and therebyto slave station 20. This is illustrated by way of a timing diagram 40shown in FIG. 2A. This first predetermined number of consecutive energypulses is shown at 42 in FIG. 2A. Consecutive energy transitions 42 arefollowed by a resting duration 44 and are preceded by a resting duration43. In a preferred embodiment of the present invention, consecutiveenergy transitions 42 are generated by master station 30 in the form ofpulses, two transitions per pulse. For the purposes of illustration,FIG. 2A shows ten such pulses for a predetermined number of 20consecutive energy transitions. During the consecutive transitions 42,slave station 20 preferably does not provide energy pulses ortransitions to coupling medium 11. During the subsequent restingduration 44, slave station 20 need not provide energy pulses ortransitions to coupling medium 11. However, in a further embodiment ofthe present invention, slave station 20 may couple one or more energytransitions to medium 11 during resting duration 44 as anacknowledgement response to indicate that it properly received the firstpredetermined number of energy transitions. This is shown at 46 in FIG.2A. Such an acknowledgement is used to increase the fault tolerance ofthe communications between master and slave stations.

Additionally, master station 30 includes means for communicating a datadigit having a second digital value to slave station 20. This includesmeans for causing a second predetermined number of consecutive energytransitions to be coupled to medium 11, and thereby to slave station 20.This is illustrated in a timing diagram 50 shown in FIG. 2B. This secondpredetermined number of consecutive energy pulses is shown at 52 in FIG.2B. Consecutive energy transitions 52 are followed by a resting duration54 and preceded by a resting duration 53. As with consecutive energytransitions 42 above, consecutive energy transitions 52 are preferablyin the form of pulses, two transitions per pulse. For the purposes ofillustration, FIG. 2B shows eleven such pulses for a predeterminednumber of 22 consecutive energy transitions. During the consecutivetransitions 52, slave station 20 preferably does not provide energypulses or transitions to coupling medium 11. During the subsequentresting duration 54, slave station 20 need not provide energy pulses ortransitions to coupling medium 11. However, in a further embodiment ofthe present invention, slave station 20 may couple one or more energytransitions to medium 11 during resting duration 54 as anacknowledgement response to indicate that it properly received the firstpredetermined number of energy transitions. This is shown at 56 in FIG.2B. Such an acknowledgement is used to increase the fault tolerance ofthe communications between master and slave stations.

The first and second predetermined numbers of energy transitions arepreferably different from one another, 20 transitions versus 22transitions. This is so that slave station 20 may distinguish betweenthe two digital values being communicated by master station 30. Withthese two digital values, master station 30 is capable of communicatingbinary digits to slave station 20 with the first and secondpredetermined numbers of consecutive energy transitions.

In an alternate embodiment according to the present invention, by usingadditional predetermined numbers of consecutive transitions differentfrom the first and second predetermined numbers, master station maycommunicate digits in numerical bases greater than 2, such as ternarydigits, quaternary digits, and decimal digits. Note also that theresting duration at the beginning of a sequence of energy transitions ispreferably the resting duration created by master station 30 after ithas transmitted a previous digital value or command to the slavestation.

System 10 further comprises means in slave station 20 for detecting frommedium 11 the first predetermined number of energy transitions 42followed by resting duration 44. This also includes means for outputtinga signal representative of the first digital value in response to thedetection of energy transitions 42. This detection means in slavestation 20 also detects the second predetermined number of energytransitions 52 followed by resting duration 54, and outputs a signalrepresentative of the second digital value in response thereto. Thesignals representative of the first and second digital values may beused to communication binary digits to slave station 20, as indicatedabove, and may be used by components within slave station 20 inprocessing or storing information. Such examples of where data is storedand/or processed within slave station 20 are provided below.

For transmitting data in the reverse direction from slave station 20 tomaster station 30, communication system 10 further comprises thefollowing means, which are illustrated by way of a timing diagram 60shown in FIG. 2C. System 10 further comprises means in master station 30for initiating a read operation from slave station 20. This includesmeans for causing a third predetermined number of energy transitions 62to be coupled to medium 11 followed by a resting duration 64. Anexemplary number of twelve energy pulses and 24 energy transitions areshown in FIG. 2C. Transitions 62 are preceded by a resting duration 63.Substantially no energy transitions are coupled to medium 11 by masterstation 30 during resting durations 63 and 64. System 10 furthercomprises means in slave station 20 for detecting from medium 11 theenergy transitions 62 followed by resting duration 64 and for outputtinga read command signal in response thereto.

System 10 further comprises means in slave station 20 responsive to theread command signal for transmitting a binary one value or binary zerovalue (i.e., third or fourth binary values) to master station 30. Thisincludes means for causing one or more energy pulses or no energy pulsesto be coupled to medium 11 by slave station 20 in a time interval duringresting duration 64 (i.e., a selected time interval), depending upon thevalue to be transmitted. These energy pulses comprise correspondingenergy transitions. A binary zero is communicated by a fourthpredetermined number of energy transitions during resting duration 64and a binary one is communicated by a fifth predetermined number ofenergy transitions during duration 64. To distinguish between the binaryzero and one values being sent, the corresponding fourth and fifthpredetermined numbers of energy transitions are different. In apreferred embodiment of the present invention, the fourth predeterminednumber is zero for a binary zero, and the fifth predetermined number isat least one energy pulse (i.e., two or more energy transitions) for abinary one. This is shown in FIG. 2C at 65 (binary zero) and 66 (binaryone).

For communicating data from slave station 20 to master station 30,system 10 further comprises means in master station 30 for detectingfrom medium 11 the number of energy pulses and/or energy transitionscoupled by slave station 20 during resting duration 64 and foroutputting a signal representative of the corresponding detected binaryvalue in response thereto. In one embodiment of the present invention,the absence of energy pulses during duration 64 indicates a binary zerovalue from slave station 20 and one or more energy pulses duringduration 64 indicates a binary one value from slave station 20. Thiscorresponds to the above described fourth and fifth predetermined numberof energy transitions. In this way, it may be appreciated that system 10comprises the means for transmitting data from slave station 20 tomaster station 30 using energy transitions (or energy pulses) coupledthrough medium 11 in the reverse direction.

The third predetermined number of energy transitions 62 may be differentfrom the first and second predetermined numbers of energy transitions 42and 52, so as to specify the direction of data flow. Alternatively, ahigh-level communication protocol may be included to specify thedirection of data flow without requiring that the third predeterminednumber be different from the first and second predetermined numbers. Anexample of such a high-level communication protocol is described belowin a further embodiment of the present invention with reference to flowdiagrams shown in FIGS. 7-14.

In addition to sending data from master station 30 to slave station 20,system 10 may, in a further embodiment, send communication commands frommaster station 30 to slave station 20 in the form of predeterminednumbers of consecutive energy transitions. Such commands may include:reading a byte of data, and writing a byte of data.

In one embodiment of the present invention, master station 30 sends a"read data byte" command, followed by an associated memory address, oridentifier, to slave station 20. The associated address is sent usingthe above write formats illustrated in FIGS. 2A and 2B for sendingdigits to slave station 20. In response, slave station 20 provides, insequential order, the digits of the requested byte, using the above readdigit format illustrated in FIG. 2C. The "read data byte" command isillustrated in FIG. 2D at graph 70, where a sixth predetermined numberof consecutive energy transitions 72 is used, and where restingdurations 73 and 74 bracket transitions 72. As an example, 26 energytransitions are shown (13 pulses). During the consecutive transitions72, slave station 20 preferably does not provide energy pulses ortransitions to coupling medium 11. During the subsequent restingduration 74, slave station 20 need not provide energy pulses ortransitions to coupling medium 11. However, in a further embodiment ofthe present invention, slave station 20 may couple one or more energytransitions to medium 11 during resting duration 74 as anacknowledgement response to indicate that it properly received the sixthpredetermined number of energy transitions. This is shown at 76 in FIG.2D. Such an acknowledgement is used to increase the fault tolerance ofthe communications between master and slave stations.

The sixth predetermined number of energy transitions 72 need not bedifferent than the other predetermined numbers 42, 52, and 62, but adifferent number may be helpful in distinguishing the command from theabove read and write formats. One example in which a different number isnot needed is where only a single read operation is performed during thetime slave station 20 is powered. Another example is where a high-levelcommunication is included (as a further embodiment) which distinguishesthe use of the fourth predetermined number from the first, second, andthird predetermined numbers. Such an example is provided below.

Also in this embodiment of the present invention, master station 30sends a "write data byte" command, followed by an associated memoryaddress, or identifier, and data byte, to slave station 20. Theassociated address and data byte are sent using the above write formatsillustrated in FIGS. 2A and 2B for sending digits to slave station 20.In response, slave station 20 stores the data byte at the specifiedlocation. The "write data byte" command is illustrated in FIG. 2E atgraph 80, where a seventh predetermined number of consecutive energytransitions 82 is used, and where resting durations 83 and 84 brackettransitions 82. As an example, 28 energy transitions are shown (14pulses). During the consecutive transitions 82, slave station 20preferably does not provide energy pulses or transitions to couplingmedium 11. During the subsequent resting duration 84, slave station 20need not provide energy pulses or transitions to coupling medium 11.However, in a further embodiment of the present invention, slave station20 may couple one or more energy transitions to medium 11 during restingduration 84 as an acknowledgement response to indicate that it properlyreceived the seventh predetermined number of energy transitions. This isshown at 86 in FIG. 2D. Such an acknowledgement is used to increase thefault tolerance of the communications between master and slave stations.

The seventh predetermined number of energy transitions 82 is preferablydifferent from the sixth predetermined number of energy transitions 72,but need not be different than the first second and third predeterminednumbers of transitions (42, 52, and 62, respectively) for the reasonsindicated above.

According to the above-described processes and device operations, datamay be transmitted from master station 30 to slave station 20 andvice-versa. There may be times in which either station 20 or station 30is processing information and, therefore, will require additional timebefore providing results to the other station. As a further embodimentof the present invention, communication system 10 further comprises anidling means for indicating that no digital data is being communicatedbetween master station 30 and slave station 20. The idling meansaccording to the present invention includes a means in master station 30for causing any other number of consecutive energy transitions to becoupled to medium 11 from master station 30.

In a preferred embodiment of the present invention, the above describedresting durations 44, 54, 64, 74, and 84 are substantially of the sametime duration. However, it may be appreciated that one or more of thesedurations may be of different durations. Additionally, the restingdurations need to be of sufficient length such that the detection meanswithin slave station 20 is enabled to distinguish the resting durationsfrom the consecutive energy transitions. As one means of distinguishingthese resting durations in a preferred embodiment of the presentinvention, each resting duration 44, 54, 64, 74 and 84 is at leastgreater than the duration between two consecutive energy transitions. Ina further preferred embodiment, each of the resting durations is equalto or greater than the time duration between three consecutivetransitions.

According to the present invention, communication system 10 preferablyfurther comprises means for initiating communications between masterstation 30 and slave station 20. Such initialization means may be usedto "synchronize" stations 20 and 30 before beginning datacommunications. To initiate communications, master station 30 generates,for example, a first missing energy pulse (i.e., a resting duration). Ifslave station 20 is ready for communications, which usually occurs afterit is sufficiently powered and after it has finished with initializingvarious means within slave station 20, slave station 20 outputs one ormore energy pulses, preferably during the missing energy pulse (restingduration), which may be detected by master station 30 as an indicationthat slave station 20 is ready for communications. Master station 30continues to periodically generate a resting duration (the missingenergy pulse) until slave station 20 issues a response. It may beappreciated that the slave station may be configured such that a largerresting duration must be detected before initialization can take place.

Depending on the operation and purpose of slave station 20, it may beappreciated that communication system 10 may be configured such thatdata can only be communicated uni-directionally from master station 30to slave station 20. It can also be configured such that data can onlybe communicated uni-directionally from slave station 20 to masterstation 30. Finally, it can also be configured to enable bi-directionaldata communication between stations 20 and 30. Similarly, commands canalso be issued from either station to the other, or bi-directionally. Anexemplary application where data is communicated only uni-directionallyfrom master station 30 to slave station 20 may be found in the field ofdiagnostic equipment. For example, master station 30 may comprise anautomobile electronics unit or a photocopying machine which communicatesessential diagnostic data to slave station 20. In this case, slavestation 20 may comprise means for receiving the diagnostic data frommaster station 30 and for providing the user with a visual displaythereof. Commands, if any, would also be communicated in this exampleuni-directionally from the master to the slave.

Exemplary applications in which data is only uni-directionallycommunicated from slave station 20 to master station 30 may be found inthe field of "simple" credit card and identification systems. Forexample, slave station 20 may comprise a means for storing an identityfor the credit card user, such as a credit card number or a securitypassword, and may communicate this user identity to master station 30for use therein. Master station 30 may comprise means for utilizing thisuser identity, such as for checking the user's credit balance in thecase of the credit card application or for checking the securityclearance of the user in a case of a security identificationapplication.

An exemplary application in which bi-directional communications betweenstations 20 and 30 is provided may be found in the so-called "debitcard" field. In this application, slave station 20 comprises a debitcard having means for storing a user balance, which may be deducted fromas the user obtains services using the debit card. In this case, masterstation 30 would comprise a means for providing services to the user,such as a photocopying machine or a transit fare collector. Inoperation, slave station 20 may first provide the current balance on thedebit card to master station 30. In response, master station 30 mayprovide services requested by the user if there are sufficient fundsindicated by the debit card to cover the requested services. Upondispensing the services, master station 30 may then transmit a newbalance to slave station 20 for recordation therein. From the aboveexamples, it may be appreciated that communication system 10 may operateto transmit data uni-directionally in either direction between a masterstation and a slave station or bi-directionally.

The above discussion of communication system 10 focused on thetransmission of data digits between stations 20 and 30. It may beappreciated that stations 20 and 30 may organize the data digits intogroups of predetermined numbers of digits, so as to support a higherlevel of overall communications. For example, control instructions anddata may be organized into groups of eight data digits, preferablybinary digits, or sixteen data digits, preferably binary digits. Theillustration of such grouping of digital data is intended to point tothe greater applicability of the present invention and is not intendedas a limitation thereof.

Because master station 30 and slave station 20 communicate by theabove-described sequences of predetermined numbers of energytransitions, all the communications between master station 30 and slavestation 20 may occur through a single electromagnetic coupling medium.This provides the advantage of enabling slave station 20 to use a singlemagnetic coil for receiving and transmitting energy transitions tocoupling medium 11 and for deriving energy to power itself. The majorityof the above-described prior art systems use two or more magnetic paths,or coupling mediums, with corresponding magnetic coils, therebycomprising expensive hybrid implementations. A further advantage ofcommunication system 10 is that the ability to use a single magneticcoil for slave station 20 readily enables an integrated circuit (IC)implementation thereof on the smallest possible chip size. An exemplaryembodiment of slave station 20 using a single coil system is describedbelow.

Related to this, it may be advantageous to use two magnetic coils in anIC chip embodiment of slave station 20, one coil for receiving energypulses and transitions from master station 30 and a second coil forsending energy transitions to master station 30. Although two coils maybe used, they preferably still use a single electromagnetic couplingmedium and need not be separated from one another by a large distance.In fact, these two coils may be disposed concentrically to one anotherto reduce the chip size of the embodiment. Further, these coils may bedisposed in an overlapping relationship as well as being concentric tofurther reduce the chip size. The use of two coils enables the coils tobe separately optimized for their particular function.

Another advantage of communication system 10 is that it enables a highlypower efficient means within slave station 20 of communicating data tomaster station 30. This highly power efficient communication meansfurther aids in enabling an integrated circuit implementation of slavestation 20 because all the energy received by slave station 20 isefficiently used, thereby reducing the required chip area needed forenergy storage. As described below in greater detail, this moreefficient means comprises an energy storage means, preferably acapacitor, which is separate from the main energy storage means forpowering slave station 20. Additionally, the separate energy storagemeans is operated to selectively discharge a substantial portion of itsenergy into the inductor means (e.g., magnetic coil) of slave station 20in a relatively short time duration to couple one or more detectableenergy transitions to medium 11. This may be done with little or noeffect on the main energy storage means for powering the components ofsalve station 20.

A more detailed embodiment of the communication system according to thepresent invention is shown at 100 in FIG. 3. Communication system 100comprises a slave station 200, a master station 300, and anelectromagnetic coupling medium 110 formed between master station 300and slave station 200. Slave station 200 corresponds to slave station 20shown in FIG. 1 and comprises the same means as disclosed above forslave station 20. Likewise, master station 300 corresponds in functionto master station 30 shown in FIG. 1, and comprises the same means asdisclosed above for master station 30. Electromagnetic coupling medium110 corresponds in function to coupling medium 11 shown in FIG. 1 and iscapable of communicating data bi-directionally between master station300 and slave station 200 in the form of electromagnetic energytransitions.

Shown in FIG. 3 is a partial block diagram and schematic diagram ofmaster station 300. Master station 300 comprises a power transmittinginductor means 310, a data receiving inductor means 320, a mastercommunication means 330, and a master digital subsystem 390. Inductormeans 310 and 320 preferably comprise at least one loop of conductivewire wound about a coil form 315. In one embodiment of the presentinvention, coil form 315 is cylindrical in nature and is formed fromferromagnetic material, such as type K-1, having a relatively highpermeability. However, form 315 may be rectangular in nature and/or maybe formed from a different material. Also in this embodiment, inductormeans 310 includes 15 to 25 turns (conductive loops) at an averageradius of ˜80 mils (˜2 millimeters). Inductor means 310 comprises afirst terminal 311 and a second terminal 312. Inductor means 320comprises a first terminal 321 and a second terminal 322. Each of theterminals of inductor means 310 and 320 are coupled to mastercommunication means 330. In turn, communication means 330 includes abi-directional data bus 336 for communicating with master digitalsubsystem 390.

As also shown in FIG. 3, slave station 200 is preferably formed on asubstrate 205 as an integrated circuit chip. Substrate 205 may comprisean insulating material, a semi-insulating material or a semiconductormaterial. In one embodiment of the present invention, substrate 205comprises a semiconductor material. Substrate 205 is preferably squareor rectangular in shape having side measurements of approximately 2.5millimeters×2.5 millimeters (i.e., 100 mils×100 mils) and a thickness ofapproximately 250 microns to 500 microns. Disposed about the outer edgeof substrate 205 is an inductor means 210 magnetically coupled tocoupling medium 110 and including a segment of conductive material 212.Inductor means 210 further comprises a first terminal 213 and a secondterminal 214 coupled at respective ends of conductive segment 212.Inductor means 210 receives magnetic energy pulses and magnetic energytransitions from coupling medium 110 and provides at terminals 213 and214 an electrical signal indicative of these energy pulses and energytransitions. In a preferred embodiment of the present invention,conductive segment 212 of inductor means 210 comprise at least one loopof conductive wire disposed on substrate 205. Two such loops are shownin FIG. 3. In one embodiment of the present invention, ten to forty suchloops are formed on substrate 205 in slave station 200 so as to providesufficient power coupling to slave station 200. The wire forming theseloops is preferably approximately 6 microns wide, with a spacing ofapproximately 2 microns between adjacent loops.

In communication system 100, the energy transitions coupled by masterstation 300 are generated according to the relationships disclosed abovewith reference to FIG. 6. Specifically, voltage cycles are coupled topower inductor means 310, each voltage cycle generating two energypulses and four energy transitions. The energy pulses and transitionsare coupled to medium 110 and generate, or induce, a voltage acrossinductor means 210 of slave station 200 which is similar in nature tothe voltage cycles being coupled to inductor means 310. This is shown,for example, by graph 504 in FIG. 6. In slave station 200, the voltagetransitions in the induced voltage are detected and counted to determinethe number of energy transitions in a set of such transitions. Asdescribed above, there is a relationship between the number ofconsecutive voltage transitions detected and the number of consecutiveenergy transitions coupled to medium 110 by master station 300.

Slave station 200 further comprises a rectifying means 220 coupled toterminals 213 and 214 of inductor means 210. Rectifier means 220generates a rectified voltage at an output port from the energy receivedby inductor means 210. Slave station 200 further comprises a powerstorage and regulation means 230 having an input port coupled to theoutput port of rectifier means 220. Means 230 comprises means forstoring electrical energy provided by the output of rectifier 220 andmeans for powering the components disposed on substrate 205 of slavestation 200. Each of rectifier means 220 and power storage andregulation means 230 are discussed below in greater detail withreference to a full schematic diagram of communication system 100 shownin FIGS. 4A and 4B.

Detector means 240 includes an input coupled to terminal 213 of inductor210. From the signal at terminal 213, detector means 240 detects voltagetransitions through zero volts (i.e., zero-crossings) and outputs asignal in response thereto as a first output. As such, detector means240 comprises means for detecting the consecutive energy transitionsbeing coupled to medium 110 by master station 300. Detector means 240further detects the absence of a voltage transition during apredetermined time duration following the detection of a precedingvoltage transition and responds by outputting an absence signal at asecond output. This corresponds to detecting the absence of an energytransition during a predetermined time duration following the detectionof a preceding energy transition. In this way, detector means 240comprises means for detecting resting durations, or times when at leastone transition is missing, such as durations 44, 54, 64, 74, and 84shown in FIGS. 2A-2E. It may be appreciated that the two signal outputsof detector means 240, the transition signal and the absence signal,enable the detection of sets of consecutive energy transitions (orvoltage transitions) coupled to slave station 200 occurring betweensuccessive resting durations.

Slave station 200 further comprises a digital subsystem 290 and acommunication means 250. Communication means 250 is responsive to theoutput signals of detector means 240, and is for counting the number ofconsecutive voltage (energy) transitions in a set of such transitions,and for outputting a command signal, a first digital value, or a seconddigital value in response thereto, depending upon the number counted.The command signal and digital values are output to digital subsystem290. Communication means 250 may also determine the duration of theresting durations occurring before and after sets of consecutive energytransitions, where these durations are unequal. Each resting duration,however, must be of a sufficient duration to enable its detection byslave station 200.

Digital subsystem 290 is for processing the commands and digital valuesthat are communicated between master station 300 and slave station 200as detected by communication means 250 and detector means 240. Asdiscussed below in greater detail, communication means 250 also receivesdata digits from subsystem 290 to be communicated to master station 300and, in response thereto, at the direction of master station 300, causesthe coupling of appropriate energy transitions to medium 110 from slavestation 200. Thus, the digital data flowing between communication means250 and subsystem 290 is reflective of the commands and digital databeing communicated between slave station 200 and master station 300. Inone embodiment of the present invention, digital subsystem comprises amemory storage means, or the like, having at least one memory storagelocation, and preferably a plurality of storage locations. Additionally,each memory storage location comprises a number of data bits, such asfor example 8 bits (one byte), and a corresponding unique address, oridentifier. Such memory storage means and the construction thereof arewell known in the art. An explanation of the construction and operationof such a memory storage means is not necessary in order to understandthe present invention and enable one of ordinary skill in the art tomake and use the same.

More specifically, a slave control means 260 in communication means 250outputs a signal to subsystem 290 on a bi-directional data bus 255representative of a first digital value when the above-described firstpredetermined number of consecutive energy transitions (cf. FIG. 2A) isdetected via the output signals of detector means 240. Control means 260further outputs a signal to digital subsystem 290 representative of asecond digital value when the above-described second predeterminednumber of consecutive energy transitions (cf. FIG. 2B) is detected. In apreferred embodiment of system 100 and slave station 200, the firstdigital value is a binary zero and the second digital value is a binaryone, and the digit thereby output to subsystem 290 is in the form of abinary digit. Also in a alternative preferred embodiment of system 100and slave station 200, the first predetermined number of energytransitions is equal to 72 (36 energy pulses, 18 voltage cycles), andthe second predetermined number of energy transitions is equal to 76 (38energy pulses, 19 voltage cycles).

Referring again to FIG. 3, communication means 250, and specificallycontrol means 260, further comprises means for receiving a data digitfrom digital subsystem 290 to be communicated to master station 300. Thedata digit provided by subsystem 290 is communicated to master station300 during the resting duration following a receipt of energy pulsesfrom master station 300 equal in number to the above-described thirdpredetermined number (cf. FIG. 2C). In this regard, control means 260further comprises means responsive to detector means 240 for detectingthe third predetermined number of consecutive energy transitionsprovided by master station 300 and for outputting a read data digitcommand signal to digital subsystem 290 in response thereto. In apreferred alternative embodiment of system 100 and slave station 200,the third predetermined number of energy transitions is equal to 80 (40energy pulses, 20 voltage cycles).

Digital subsystem 290 responds to the read data digit command signal byproviding control means 260 with a data digit on the bi-directional databus 255. Communication means 250 further comprises a transmission meansfor transmitting the data digit provided by subsystem 290 to masterstation 300 during the resting duration, or transition absence,following the detection of the third predetermined number of energytransitions signaling the read operation. This transmission meanscomprises portions of control means 260, a capacitor 280 for storingelectrical energy in the form of electrical charge, and a switch matrix270 for selectively charging capacitor 280 from the energy rectified byrectifier means 220 and for selectively coupling capacitor 280 toinductor means 210.

In response to the detection of the third predetermined number of energytransitions from master station 300, the transmission means causes apredetermined number of energy transitions to be coupled to inductormeans 210 in a time interval during the subsequent resting duration(transition absence), the number being related to the value of thedigital data provided by digital subsystem 290. In a preferredembodiment of the present invention, control means 260 directs switchmatrix 270 to couple capacitor 280 to inductor means 210 when the valueof the data digit provided by subsystem 290 is a binary one. This causescapacitor 280 to discharge its stored charge into inductor means 210 andcauses at least one energy transition, preferably at least two energytransitions, to be coupled from slave station 200 to coupling medium110. More specifically, capacitor 280 and inductor means 210 form adamped resonant circuit which causes voltage cycles to be applied acrossinductor means 210. The voltage cycles generate energy pulses and energytransitions in a similar manner as that described above with referenceto FIG. 6.

When the value of the data digit supplied by digital subsystem 290 is abinary zero, control means 260 directs switch matrix 270 to isolate, orprevent, capacitor 280 from being discharged into inductor means 210. Inthis case, substantially no energy transitions are coupled from slavestation 200 to medium 110. In a preferred embodiment of the presentinvention, capacitor 280 is charged, via switch matrix 270, by energyprovided by rectifier means 220 such that an mount of charge is storedon capacitor 280. The charging occurs when capacitor 280 is not neededfor discharging energy into inductor means 210. In a further embodimentof system 100, control means 260 outputs a read-byte command to digitalsubsystem 290 when a sixth predetermined number of consecutive energytransitions (cf. FIG. 2D) is detected. In a preferred alternativeembodiment of system 100 and slave station 200, the sixth predeterminednumber of energy transitions is equal to 84 (42 energy pulses, 21voltage cycles). In response to this, digital subsystem 290 prepares toreceive an address which identifies the particular byte of data masterstation 300 is requesting from the memory of digital subsystem 290. Thisaddress is provided to slave station 200 in a sequence of data digits,preferably binary digits, where each data digit is communicated by acorresponding set of consecutive energy transitions as described above(cf. FIGS. 2A and 2B). The address is provided to digital subsystem 290,which outputs a corresponding data byte to control means 260. To receivethe data byte, master station couples a sequence of eight sets ofconsecutive energy transitions, each set having a third predeterminednumber of transitions (cf. FIG. 2C). Control means 260 communicates, insequential order, each bit from the data byte in a corresponding restingduration of these eight sets of consecutive energy transitions.

In a further embodiment of system 100, control means 260 outputs awrite-byte command to digital subsystem 290 when a seventh predeterminednumber of consecutive energy transitions (cf. FIG. 2E) is detected. In apreferred alternative embodiment of system 100 and slave station 200,the seventh predetermined number of energy transitions is equal to 88(44 energy pulses, 22 voltage cycles). In response to this, digitalsubsystem 290 prepares to receive an address which identifies thelocation within the memory of digital subsystem 290 where the byte is tobe written. This address is provided to slave station 200 in a sequenceof data digits, preferably binary digits, where each data digit iscommunicated by a corresponding set of consecutive energy transitions asdescribed above (cf. FIGS. 2A and 2B). The address is provided todigital subsystem 290. Following the address, the data byte iscommunicated to slave station 200 one digit at a time and provided todigital subsystem 290 in a manner as described above.

Each of the respective components of slave station 200 and masterstation 300 are described in greater detail with respect to the morespecific schematic diagram of communication system 100 shown in FIGS. 4Aand 4B. As seen in FIGS. 4A and 4B, communication system 100 is shownwith slave station 200 and master station 300 being separated by aboundary line B. Inductor means 210 of slave station 200 is representedby a coil symbol at the reference numeral 210, which is disposed nearboundary line B. Likewise, inductor means 310 and 320 of master station300 are represented by respective coil symbols at reference numerals 310and 320, respectively. The coil symbols for inductor means 310 and 320are disposed near boundary line B and positioned opposite to that forinductor means 210. Coupling medium 110 is disposed between therespective inductor means of slave station 200 and master station 300,as indicated in FIGS. 4A and 4B.

It should be appreciated that, for the purposes of modeling the couplingof energy between inductor means 210 and inductor means 310 and 320,these inductor means may be viewed as forming a transformer. It shouldbe pointed out, however, that such a transformer need not be an idealtransformer, and, in practice, may often be less than ideal due to corelosses, core reluctance, parasitic resistance in the inductor means, lowmagnetic coupling between the windings of the inductor means, and due tothe gap between inductor means 310, 320 and inductor means 210, whichmay be on the order of zero to sixteen millimeters or more. Atransformer model having sufficient parasitic leakage inductance,winding resistances, core loss resistances, and low coupling may be usedto model the inductive interaction between inductor means 210 andinductor means 310, 320 according to the present invention. Anexplanation of the operation of a conventional transformer formed bythese inductor means is not necessary in order to understand the presentinvention and enable one of ordinary skill in the art to make and usethe same. For a further discussion of transformer interaction, referenceis made to the monographs by Adam C. Malamy, "A Magnetic Power andCommunications Interface for Pinless Integrated Circuits", MassachusettsInstitute of Technology, September 1987, and by Charles W. Selvidge, "AMagnetic Communication Scheme for Integrated Circuits", MassachusettsInstitute of Technology, June 1987.

Turning now to master station 300 as shown in FIG. 4A, mastercommunication means 330 of master station 300 comprises an oscillator340, a gating transistor 350, a driver stage 355, a master control means360, a transition sensing means 370, a current sense resistor 385, and adifferential amplifier 380. Oscillator 340 generates voltage cycleswhich are buffered by driver stage 355 and coupled to inductor means310. Under the direction of master control means 360, gating transistor350 selectively grounds the voltage cycles produced by oscillator 340 soas to selectively introduce resting periods in the energy transitionscoupled to medium 110 by master station 300, thereby delineating sets ofconsecutive energy transitions. Master control means 360, in response tocommands received by digital subsystem 390, directs the communication ofinformation between stations 30 and 20 by coupling sets of consecutiveenergy transitions to medium 110 and by receiving responses back fromslave station 20 by way of inductor means 320. Current sense resistor385 and amplifier 380 monitor the current through inductor means 310 andgenerate a signal indicative of the current zero-crossings therein sothat the voltage drive to inductor means 310 can be shut off under zerocurrent conditions. Transition sensing means 370 is coupled to inductormeans 320 and is for detecting the magnetic energy transitions receivedby master station 300 from coupling medium 110. The detected energytransitions are provided to master control means 360.

In a preferred embodiment of the present invention, energy pulses andenergy transitions are coupled to medium 110 by master station 300 bythe application of voltage cycles to a magnetic coil (inductor means310) as discussed above with reference to FIG. 6. Oscillator 340preferably outputs a continuous sinusoidal voltage signal at an outputport 341, which is coupled to the input of driver stage 355. In oneembodiment of master station 300, the signal at output port 341alternates between a first voltage of -10 V and a second voltage of +10V, has a duty cycle of substantially 50%, and has an oscillationfrequency in the range of 0.5 MHz to 10 Mhz, preferably 5 Mhz. In otherembodiments of master station 300, the peak-to-peak voltage at outputport 341 is increased towards 40 V (-20 V for the first voltage and +20V for the second voltage) in order to increase the power coupling toslave station 200. Oscillator 340 further comprises a second output port342 for outputting a synchronization signal to an input port 362 ofmaster control means 360. The synchronization signal has digital logiclevels and is preferably a square wave having the same frequency ormultiple (e.g., 2, 3, 4, . . . ) or sub-multiple (e.g., 1/2, 1/3, 1/4, .. . ) thereof. Additionally, the synchronization signal preferablycomprises logic transitions representative of the zero-voltage crossingin the signal at output port 341. This enables control means 360 toinitiate a set of consecutive voltage cycles starting at a voltage valueof zero volts. In one embodiment of the present invention, thesynchronization frequency has the same frequency as the signal at outputport 341, has a duty cycle of 50%, and is substantially in phase withthe signal at output port 341 (i.e., it has a low-to-high logictransition when the signal at output port 341 begins its positive halfcycle).

Output driver 355 preferably comprises an NMOS transistor 356 and a PMOStransistor 357, which are coupled in a standard push-pull,source-follower output-stage configuration. The voltage gain of driverstage 355 is slightly less than one, but the power gain is substantiallymore than one. The gates of transistors 356 and 357 are coupled togetherat the input of driver stage 355 and the source terminals are coupledtogether at the output of driver stage 355. The drain of NMOS transistor356 is coupled to the +V_(PP) supply and the drain of PMOS transistor357 is coupled to the -V_(PP) supply. The -V_(PP) level has a value nearthat of the first voltage level of oscillator output 341 and the +V_(PP)has a value near that of the second voltage level of oscillator output341. In turn, the output of the driver stage 355 is coupled to firstterminal 311 of power inductor means 310 by way of current senseresistor 385. Second terminal 312 of power inductor means 310 is coupledto ground. (As an alternative, second terminal 312 may be driven by asignal which is 180° out of phase with the signal coupled to firstterminal 311.) With this coupling, the signal from oscillator 340 iscoupled to power inductor means 310, for coupling of energy pulses andenergy transitions to medium 110.

Gating transistor 350 comprises a first conduction terminal (e.g., a FETdrain) coupled to output port 341 of oscillator 340 and to the input ofdriver stage 355, a second conduction (e.g., a FET source) terminalcoupled to ground, and a control terminal (e.g., a FET gate) coupled toa first output port 361 of control means 360. Caring transistor 350serves to selectively ground the input signal to driver stage 355, whichresults in an output voltage of substantially zero volts, due to thenear unity voltage gain of stage 355. This occurs when gating transistor350 is rendered conductive by a voltage of approximately 5 to 10 voltsapplied to its control terminal (gate). As a result, the signal coupledto power inductor means 310 by driver stage 355 is substantially zero.Gating transistor 350 is rendered non-conductive when a voltage ofapproximately -V_(PP) is applied to its control gate. When this occurs,the signal generated at output port 341 is coupled to the input ofdriver stage 355 and on to inductor means 310.

The control terminal (e.g., gate) of transistor 350 is responsive to acontrol signal generated on an output port 361 by control means 360.Depending upon the state of communications between master station 300and slave station 200, control means 360 selectively renders transistor350 conductive so that one or more energy transitions from oscillator340 are prevented from being coupled to inductor means 310. In thismanner, control means 360 is enabled to selectively place restingdurations between sets of consecutive energy transitions provided byoscillator 340.

As indicated above, resistor 385 is coupled between the output of driverstage 355 and terminal 311 of inductor means 310 and is for sensing theinstantaneous current through inductor 310. As indicated above withreference to FIG. 6, the current through inductor means 310 is cosine innature. In turn, the voltage generated across resistor 385 is cosine innature. Differential amplifier 380 includes a non-inverting input 381and an inverting input 382, each coupled to a respective terminal ofresistor 385, and an output 383 coupled to an input 363 of control means360. The value of resistor 385 is preferably chosen such that a voltagehaving a peak-to-peak value of at least ˜100 mV is generated between theinputs 381,382 of amplifier 380. In one embodiment of the presentinvention, where the inductance of inductor 310 is ˜10 μH and thefrequency of oscillator 340 is ˜5 MHz, the value of resistor 385 is onthe order of 1 to 2 ohms. With this level of input, amplifier 380generates a square wave analog of the current waveform at its output383. The signal at output 383 comprises zero-voltage crossings whichindicate when the current in inductor 310 is substantially zero. Mastercontrol means 360 monitors the zero-voltage crossings and preferablycomprises a zero-voltage crossing detector.

Master control means 360 is responsive to communication commands issuedby digital subsystem 390 and comprises means for controlling theoperation of gating transistor 350 to provide appropriate sets ofconsecutive energy transitions to medium 110, as specified by a givencommunication protocol. An exemplary communication protocol is describedbelow. Control means 360 additionally includes input port 362 forreceiving the synchronization signal from oscillator 340, input port 363for receiving the zero-current sense signal from amplifier 380, an inputport 366 for receiving a detection indication signal from sensing means370, and an input/output port 364 coupled to a bi-directional data bus336 for receiving commands from digital subsystem 390. Data bus 336 is,in turn, coupled to an input/output port 396 of digital subsystem 390.Master control means 360 further includes output port 361 for outputtinga gating signal to transistor 350, and an output port 367 for outputtinga control signal to transition sensing means 370, which is described ingreater detail below.

In this regard, it may be appreciated that the electricalcharacteristics of oscillator 340, driver stage 355, and inductor means310 can be characterized to determine the steady-state phase differencebetween the voltage signal at oscillator output 341 and the currentthrough inductor means 310. The current typically lags the voltagesignal at a phase angle ranging between ˜0° and ˜90°, depending upon theamount of parasitic resistance, capacitance, and core losses. With aknown phase difference and a known oscillation frequency, control means260 can turn off the voltage to inductor means 310 under a zero currentcondition by turning off the voltage at a predetermined time, asdetermined by the frequency and phase angle, after a zero-voltagecrossing in the signal at oscillator output 341. In this case, it may beappreciated that this predetermined turn-off time would serve the samefunction as current sense resistor 385 and buffer amplifier 380, andthat it could be used as a replacement thereof.

Master control means 360 further comprises means responsive to thesignal at input port 362 for initiating a set of consecutive energytransitions when the voltage of oscillator output 341 is near zero voltsand means responsive to the signal at input port 363 for terminating aset of consecutive energy transitions when the current through inductor310 is near zero amperes. The initiating means includes means forgenerating a voltage of ˜-V_(PP) at output port 361 at the beginning ofeach set of transitions and throughout the set of transitions. Thetermination means includes means for generating a voltage of between ˜5volts and +V_(PP) at output port 361 at the end of each set oftransitions and before each set. The means for generating the voltagesat output port 361 may be accomplished by digital circuitry andlevel-shifting circuitry well known in the digital circuits art.

Master control means 360 further comprises means for communicating withdigital subsystem 390 by way of data bus 336. Both communicationcommands and bi-directional data are capable of being communicatedbetween control means 360 and digital subsystem 390 over bus 336. Anyone of the many well known data bus communication protocols such asRS232, μWIRE, SPI, I² C, or byte-wide transfer may be used forcommunicating between control means 360 and digital subsystem 390. Thechoice of such a protocol and a detailed description thereof is notcritical to an understanding of the present invention and to enable oneof ordinary skill in the art to make and use the same.

As indicated above, transition sensing means 370 is for detecting themagnetic energy transitions received by master station 300 from couplingmedium 110 by way of inductor means 320. Transition sensing means 370comprises a differential amplifier 378, two resistors 371 and 372, ananalog switch 374 having a PMOS transistor and an NMOS transistor, andan invertor 375 for driving the gate of the PMOS transistor of analogswitch 374. Differential amplifier 378 includes a non-inverting inputand an inverting input, which are coupled to terminals 321 and 322 ofinductor means 320, respectively, by way of resistors 371 and 372,respectively. In one embodiment, terminal 322 is coupled to ground toreference the voltage generated by inductor means 320. The magneticenergy transitions received by inductor means 320 are coupled toamplifier 378 in the form of electrical signals, preferably voltagesignals, which are then amplified at an output of amplifier 378. Theoutput of differential amplifier 378 is coupled to input port 366 ofcontrol means 360, which provides control means 360 with an indicationthat energy transitions have been coupled to master station 300. Thenumber of energy transitions is preferably determined by counting thenumber of voltage transitions occurring at the output of amplifier 378.In a preferred embodiment of system 100, the occurrence of notransitions at the output of amplifier 378 during a resting duration 64represents a binary zero value and the occurrence of one or morerepresents a binary one value. These transitions are readily detected bycontrol means 360 at input port 366.

Switch 374 of sensing means 370 is for selectively coupling theinverting and non-inverting inputs of amplifier 378 together such thatamplifier 378 is prevented from providing an indication of any energytransitions. In a preferred embodiment of the present invention, analogswitch 374 is rendered conductive to prevent amplifier 378 fromindicating transitions during those times in which master station 300 iscoupling energy transitions to medium 110, and to avoid over-driving thesensitive inputs of amplifier 378 with the relatively large signalgenerated by inductor means 310 of the master station itself. Sensingmeans 370 is enabled to only detect those energy transitions provided tocoupling medium 110 by slave station 200. In this regard, it may beappreciated that, as an equivalent, analog switch 374 may be omitted andan equivalent function placed within control means 360, whereby thesignal at second input 366 is only monitored by control means 360 duringresting durations, e.g., at times when control means 360 has renderedgating transistor 350 conductive. This may be done in cases whereamplifier 378 comprises inputs which can tolerate the large signalgenerated by indictor means 310.

As an alternative to coupling the inputs of amplifier 378 to inductormeans 320, these inputs may be coupled to inductor means 310, providedthat driver means 355 is electrically isolated from inductor means 310during the resting durations.

For selectively gating analog switch 374, sensing means 370 preferablycomprises an invertor 375 having an input coupled to the gate of theNMOS transistor of analog switch 374 and an output coupled to the gateof the PMOS transistor. Second output port 367 of control means 360 iscoupled to the gate of the NMOS transistor of analog switch 374 and tothe input of invertor 375. To selectively render analog switch 374conductive, control means 360 raises the voltage on output port 367 tosubstantially greater than three volts, which causes both the PMOS andNMOS transistors of analog switch 374 to become conductive. To renderthe PMOS and NMOS transistors of analog switch 374 nonconductive,control means 360 places a negative voltage on the order of -V_(PP) onoutput port 367.

The operation of control means 360 is further described below withreference to a flow diagram shown in FIGS. 6A-6C. However, a furtherdescription of slave station 200 is first provided.

A more specific schematic diagram of slave station 200 is also shown inFIG. 4B. Each of rectifier means 220, power and regulation means 230,detector means 240, communication means 250, and digital subsystem 290are discussed below in greater detail. Rectifier means 220 includes afirst port having terminals 221 and 222 coupled to terminals 213 and214, respectively, of inductor means 210, and an output port havingterminals 223 and 224. Rectifier means 220 comprises means forgenerating a rectified voltage at its output port from the energyreceived at its input port from inductor means 210. Rectifier means 220further comprises four transistors 225a, 225b, 225c, 225d configured ina conventional full-wave bridge rectifier topology. In a preferredembodiment of the present invention, transistors 225a-d comprise NMOStransistors. Rectifier means 220 generates a rectified voltage andcurrent at its output port from the energy received by inductor means210. Transistors 225a-d are configured such that a positive voltage isdeveloped at terminal 223 with respect to terminal 224. As shown in FIG.4B, terminal 223 is coupled to a power storage capacitor 234 ofregulator 235.

Power and regulation means 230 includes an input port having terminals231 and 232 coupled to the output port of rectifier means 220.Specifically, input terminal 231 is coupled to output 223 of rectifiermeans 220 and input terminal 232 is coupled to output 224 of rectifiermeans 220. Power and regulation means 230 further includes an outputport including a terminal 236 for providing a positive voltage supplyV_(DD), a terminal 239 for providing a negative voltage supply -V_(BB),and a terminal 237 for providing a ground reference potential. The powersupplies and ground provided by means 230 are used to provide therequisite power for detector means 240, communication means 250, anddigital subsystem 290 of slave station 200. Power and regulation means230 comprises a power storage capacitor 234 coupled between inputterminals 231 and 232 for storing electrical energy generated byrectifier means 220. Power and regulation means 230 preferably furtherincludes a regulation means 235 having an input coupled to capacitor234, an output coupled to terminal 236, and a grounding port coupled toinput terminal 232 and to ground terminal 237. As shown in FIG. 4B,input terminal 232 is coupled to ground terminal 237. Exemplaryregulation means are well known in the an and a more detailed discussionof such means is not necessary in order to understand the presentinvention and enable one of ordinary skill in the an to make and use thesame.

Power and regulation means 230 preferably further includes a negativevoltage generation means 238 having an input coupled to capacitor 234and an output coupled to terminal 239. An exemplary negative voltagegeneration means may include a charge pump, as for example taught inU.S. Pat. No. 4,393,481 to Owen, et al. A more detailed discussion ofsuch a negative voltage generation means is not necessary in order tounderstand the present invention and enable one of ordinary skill in thean to make and use the same. It may be appreciated that rectifier means220 and capacitor 234 comprise means for powering slave station 200 andthat regulation means 235 and 238 comprise means for providing regulatedpower supplies to slave station 200.

In one preferred embodiment of the present invention, regulation means235 comprises means for limiting the maximum voltage provided at outputterminal 236 to a predetermined voltage, for example 6 V. Suchregulation means are well known to the solid state circuits an and adetailed explanation thereof is not necessary in order to understand thepresent invention and enable one of ordinary skill in the an to make anduse the same. Regulation means 235 may further include ansource-follower type output stage which regulates the voltage of itsoutput to approximately 5 V and enables the voltage at its input (i.e.,capacitor 234) to rise to voltages well above 5 V, thus enablingcapacitor 234 to store greater amounts of energy.

Detector means 240 includes a first input terminal 243, a first outputport 241, a second output port 242, a power receiving terminal 244, anda ground terminal 245. As indicated above, inductor means 210 receivesmagnetic energy transitions from medium 110 and provides at itsterminals 213 and 214 an electrical signal indicative of these magneticenergy transitions. Input port 243 of detector means 240 is coupled toinductor means 210 and is for receiving this electrical signalindicative of the magnetic energy transitions received by inductor means210. Detector means 240 comprises means for detecting from theelectrical signal provided to input port 243 an energy transition andfor outputting a transition signal in response thereto at its firstoutput port 241. Detector means 240 further comprises means fordetecting, from the electrical signal at input 243, the absence of anenergy transition during a predetermined time duration following thedetection of a preceding energy transition and for outputting an absencesignal in response thereto at its second output port 242.

For detecting the absence of an energy transition, detector means 240further includes means for comparing the time duration betweensuccessive detected transitions against a predetermined time durationand for generating the absence signal at output port 242 when the timeduration between two successive transitions exceeds this predeterminedtime duration. In operation, consecutive energy transitions received byslave station 200 occur substantially within a set predetermined timeT_(ET). If an energy transition does not occur within the time durationT_(ET) from the last detected transition, then an absent transition isindicated. In one embodiment of detector means 240, an absence signal isgenerated if such an energy transition does not occur within a timeduration of 2*T_(ET), which is equal to the time duration between threeconsecutive transitions. This longer time is to provide a "safety"margin for the detection of absent transitions since master station 300and slave station 200 may be operating with slightly different timebases. It may be appreciated that any time duration greater than T_(ET),such as 3/2*T_(ET), may also be used.

An exemplary embodiment of detector means 240 is shown at 400 in FIG.5A. Ports 241-243 of detector means 240 are replicated for detectormeans 400. Detector means 400 comprises a zero-voltage crossing detector405 for detecting zero-voltage crossings in the signal present at port243 and for outputting corresponding pulses at an output 407, which iscoupled to port 241. Zero-crossing detector 405 includes an input 406coupled to input port 243. Detector means 400 further comprises aninterval timer 410, including an input 411 and an output 412, forgenerating a predetermined time-out period. Input 411 is coupled tooutput 407 of detector 405 and output 412 is coupled to port 242 by wayof a digital inverter 415. In response to a pulse at its input 411,interval timer 410 generates a negative-going pulse (high-low-high) apredetermined time interval later. If another pulse is received at input411 before this time interval is elapsed, the timer is reset. In thiscase, a negative-going pulse is not generated. In this way, anegative-going pulse is generated if the time between pulses at input411 is greater than the timer interval. The timer interval is set to begreater than the time T_(ET) and, in a preferred embodiment, greaterthan 2*T_(ET). For convenience, the negative-going pulse at output 412is inverted to a positive going pulse (low-high-low) by inverter 415before being coupled to output port 242.

Exemplary waveforms of the signals at ports 241-243 are shown in timingdiagram 425 in FIG. 5B. Timing diagram 425 includes a graph 426 showingan exemplary voltage V₂₄₃ at port 243, a graph 427 showing an exemplaryvoltage V₂₄₁ at port 241, a graph 428 showing an exemplary voltage V₂₄₂at port 242, and a graph 429 showing the energy pulses and transitionscorresponding to input signal V₂₄₃. Two sets of consecutive voltagecycles separated by a resting duration 430 are shown in graph 426. Alsoshown in graph 426 are a positive threshold level 431 and a negativethreshold level 432, which are used in detecting the zero voltagecrossings in signal V₂₄₃. In a preferred embodiment of the presentinvention, a pulse is generated at output 407 of detector 405 when apositive-going transition in V₂₄₃ (i.e., negative to positive) crossespositive threshold 431, and a pulse is generated at output 407 when anegative-going transition in V₂₄₃ (i.e., positive to negative) crossesnegative threshold 432. The corresponding pulses at shown at graph 427.In a preferred embodiment, the last voltage transition in a set ofvoltage cycles, shown at 433 in FIG. 5B, does not generate a pulsebecause it does not cross through negative threshold level 432.Threshold levels 431 and 432 aid in mitigating the effects of noise,which may cause an unwanted pulse indication. These levels are alsoshown in graph 504 of FIG. 6.

The time period T_(ET) between energy transitions in graph 429 are shownat 435 in graph 429. The missing pulse signal V₂₄₂ generated in responseto resting duration 430 is shown at 440 graph 428. As can be seen bycomparing graphs 428 and 429, pulse 440 occurs slightly more than2*T_(ET) after the last energy transition preceding resting duration430. In a preferred embodiment of the present invention, there are twozero-voltage crossings detected for each voltage cycle (graph 426).Thus, the number of zero crossings N_(ZVC) detected is twice the numberof voltage cycles N_(VC) :N_(ZVC) =2*N_(VC). In each set of consecutivevoltage cycles, the number of zero-crossing detection pulses (graph 427)is equal to twice the number of voltage cycles plus one due to the pulsegenerated in response to the partial voltage cycle at the end of theset, which is shown at 434 in graph 426. Thus, the number of pulses,N_(PULSES), output on port 241 for a set of consecutive energytransitions is equal to (2*N_(VC) +1). As indicated above, there arefour energy transitions per voltage cycle, N_(ET) =4*N_(VC). Thus, thenumber of pulses output on port 241 can be directed related to thenumber of energy transitions in medium 110 as: N_(PULSES) =(1/2*N_(ET)+1).

Both zero-voltage crossing detector 405 and interval timer 410 may beconstructed by circuits well known in the digital circuits art. Forexample, detector 406 may comprise a dual edge-triggered monostablemultivibrator ("one-shot") having an output pulse duration which isshorter than the time between zero-crossings. Interval time 410 maycomprise an edge triggered monostable multivibrator timer. Suchcircuitry are well known in the art and a further detailed explanationthereof is not necessary in order to understand detector means 400 (and240) and enable one of ordinary skill in the art to make and use thesame. Thus, it may be appreciated and detector means 240 comprise adetection means coupled to the first and second terminals of inductormeans 210 for detecting from the electrical signal of inductor means 210an energy transition and outputting a transition signal at output port241 in response thereto. It may also be appreciated that this detectionmeans is further for detecting the absence of an energy transitionduring a predetermined time duration following the detection of apreceding energy transition and for outputting an absence signal atoutput 242 in response thereto.

Returning now to FIG. 4B, communication means 250 includes an input port251 for receiving the transition signal from detector means 240, aninput port 252 for receiving the absence signal from detector means 240,output ports 253 and 254 for providing energy transitions to inductormeans 210, a bi-directional communications bus 255 for communications toand from digital subsystem 290, and a power port 259 for receiving powerfrom power means 230. Ports 251 and 252 are coupled to output ports 241and 242, respectively, of detector means 240. Ports 253 and 254 arecoupled to terminals 213 and 214, respectively, of inductor means 210.Bus 255 is coupled to a corresponding port 295 of digital subsystem 290.Power port 259 is coupled to output terminal 236 of power and regulationmeans 230.

Control means 260 of communication means 250 is responsive to thetransition and absence signals from detector means 240 and includes aninput port 261 coupled to output port 241 (by way of port 251) forreceiving the transition signal, and an input port 262 coupled to outputport 242 (by way of port 252) for receiving the absence signal.Additionally, control means 260 comprises means for detecting, i.e.,counting, the number of consecutive energy transitions occurring betweena first absence of energy transitions and a subsequent second absence ofenergy transitions. Control means 260 preferably comprises a countermeans responsive to the signals at ports 241 and 242 for this purpose.Control means 260 further includes output ports 263 and 264 coupled toswitch matrix 270 for directing the operation of matrix 270, and acommunications port 265 coupled to bus 255 for communicating data todigital subsystem 290. Control means 260 further includes a power port269 coupled to V_(DD) supply terminal 236, a negative voltage port 268coupled to -V_(BB) supply terminal 239, and a ground port 267 coupled toground 237. As discussed below in greater detail, control means 260further comprises means for outputting digital data to digital subsystem290 and for receiving digital data from subsystem 290 via port 265, andmeans for directing switch matrix 270 to charge capacitor 280 from theV_(DD) supply terminal 236 and to selectively discharge capacitor 280into inductor means 210 via port 253 and 254.

Switch matrix 270 comprises a first node 274, a second node 275, andfour transistors 276-279. A respective terminal of capacitor 280 iscoupled of each of nodes 274 and 275. The two conduction terminals oftransistor 276 (e.g., source and drain) are coupled to node 274 andoutput port 253 of the communication means 250, respectively. Thecontrol terminal of transistor 276 (e.g., gate) is coupled to outputport 263 of control means 260. Likewise, the two conduction terminals oftransistor 277 (e.g., source and drain) are coupled to node 275 andoutput port 254 of communication means 250, respectively. The controlterminal of transistor 277 (e.g., the gate) is also coupled to outputport 263 of control means 260. Transistors 276 and 277 are responsive tooutput port 263 and provide means for coupling capacitor 280 to inductormeans 210 via ports 253 and 254 when a positive voltage is applied byoutput port 263. The discharge of capacitor 280 into inductor means 210couples at least one energy transition, and preferably at least twoenergy transitions, from inductor means 210 into coupling medium 110.When capacitor 280 is to be isolated from inductor means 210, outputport 263 applies a negative voltage to the control terminals oftransistors 276 and 277 to keep these transistors turned OFF. This isbecause the voltage at each of terminals 213 and 214 alternate betweenpositive and negative values with respect to ground 237.

In a similar manner, the conduction terminals of transistor 278 (e.g.,source and drain) are coupled to node 274 and ground, respectively. Thecontrol terminal of transistor 278 (e.g., gate) is coupled to outputport 264 of control means 260. Likewise, the conduction terminals oftransistor 279 (e.g., source and drain) are coupled to node 275 andV_(DD) supply terminal 236, respectively. The control terminal oftransistor 279 (e.g., the gate) is coupled to output port 264 of controlmeans 260. Transistors 278 and 279 are responsive to output port 264 andprovide means for coupling capacitor 280 between ground and the V_(DD)supply terminal 236 for selectively charging capacitor 280 when apositive voltage is applied by output port 264. In a preferredembodiment, transistors 278 and 279 collectively have an initial "ON"resistance which is sufficiently high to prevent the charging ofcapacitor 280 from excessively loading the supply voltage V_(DD),thereby maintaining V_(DD) at a sufficient level for operating the othercomponents of slave station 200. The sufficient "ON" resistance may beaccomplished in a number of ways. First, either one or both transistors278 and 279 may be designed with a lower W/L ratio (channel-width tochannel-length). Second, the gate drive to transistors 278 and 279 maybe gradually ramped up, or otherwise modulated. Third, the gate drivemay be pulsed.

When capacitor 280 is coupled to inductor means 210, a resonantdistributed LC circuit is formed whereby energy may be transferred backand forth between capacitor 280 and inductor means 210. In oneembodiment of slave station 200, the distributed LC circuit of inductormeans 210 and discharge capacitor 280 have a resonant frequency ofapproximately 30 Mhz, which is greater than the preferred range ofoscillation frequency of 0.5 Mhz to 10 Mhz for oscillator 340 of masterstation 300. Additionally in this embodiment, inductor means 210 has aparasitic resistance of 2K-ohms to 4K-ohms (lumped equivalent), aninductance of 5 to 10 micro-henries (lumped equivalent), and acapacitance of approximately 5-10 picofarads (lumped equivalent), andcapacitor means 280 has a capacitance of 10-20 picofarads (lumpedequivalent). With these parameters, the distributed RLC circuit has anover-damped response characteristic, which limits the number of voltageand current oscillations that occur between capacitor 280 and inductormeans 210 when capacitor 280 is discharged into inductor means 210. Alsoin this preferred embodiment of communication system 100, master station300 provides resting durations equal to at least one pulse duration ofoscillator 340. Thus, with this limited number of oscillations in theslave's LC circuit and with the resonant frequency of the slave's LCcircuit being larger than the preferred frequency range of oscillator340, slave station 200 is capable of coupling a limited number oftransitions, preferably at least two, during the above-described thirdresting duration.

An alternate embodiment of slave station 200 is shown at 200' in FIG.4C. Slave station 200' is identical to slave station 200 shown in FIG.4B with the exception that a second inductor means 210' is used indischarging storage capacitor 280. Second inductor means includes afirst terminal 213' coupled to port 253 of communication means 250 and asecond terminal 214' coupled to port 254 of communication means 250.Second inductor means 210' is coupled to electromagnetic coupling medium110 and may be constructed in a similar manner as inductor means 210.Inductor means 210 and 210' may comprise coils which are separatelydisposed from one another or are disposed concentrically. The case whereinductor means 210 and 210' are disposed separate from one another isshown at 1000 in FIG. 16A, and the case where inductor means 210 and210' are disposed concentrically to one another is shown in FIG. 16B. Inorder to reduce the visual complexity of FIGS. 16A and 16B, twoexemplary loops of conductive wire for each of inductor means 210 and210' are shown in FIG. 16A and an exemplary single loop of conductivewire for each of inductor means 210 and 210' is shown in FIG. 16B. Theuse of two such coils 210 and 210' provides the advantage of enablingthe design optimization of each coil for its respective function.

Having thus described slave station 200, the following points may now beappreciated. First, it may be appreciated that capacitor 234 comprises afirst energy storage means for storing energy in an electrical form andthat inductor means 210 and transistors 225a-d collectively comprisemeans for coupling the energy from the energy pulses coupled to slavestation 200 to the first energy storage means. It may be furtherappreciated that capacitor 280 comprises a second energy storage mediumand that control means 260 and switch matrix 270 collectively comprisemeans for charging capacitor 280 (the second energy storage means) fromthe energy stored in capacitor 234 (the first energy storage means). Itmay also be appreciated that control means 260 and switch matrix 270collectively comprise means for selectively coupling the energy storedin capacitor 280 to inductor means 210 during a selected time interval(such as, for example, during a portion of a resting duration) to causeat least one energy transition to be coupled to medium 110. Nearly allthe charge stored on capacitor 280 may be coupled to inductor means 210in a relatively short time duration without substantially affecting thecharge stored on capacitor 234, which powers the components of slavestation 200. The short time duration is preferably less than the averagetime duration of the above-described numbers of consecutive energytransitions. As compared with the prior methods of communicatinginformation from a slave station to a master station, this is a highlypower efficient way of coupling energy transitions to medium 110 whichmay be readily detected by master station 300. With this greaterefficiency, slave station 200 may be readily formed on an integratedcircuit chip because all the energy received by slave station 20 isefficiently used, thereby reducing the required chip area needed forenergy storage.

The operation of control means 360 of master station 300 and controlmeans 260 of slave station 200 are now further described with referenceto flow diagrams shown in FIGS. 7-14.

A flow diagram of the operation of an exemplary master control means 360for master station 300 according to the present invention is shown at600 in FIG. 7. Flow diagram 600 comprises blocks 602-626, beginning atblock 602 and ending at block 626. In blocks 604 through 612, mastercontrol means 360 receives a command from digital subsystem 390 andinitializes communications with a slave station 200. In blocks 614-624,master control means 360 interprets the communication command fromsubsystem 390, executes the communication command, and then checksdigital subsystem 390 for further communication commands. In a preferredembodiment of the present invention, the communication commands include,but are not limited to, a read-byte command which requests a byte ofdata from slave station 200, and a write-byte command, which sends abyte of data to slave station 200 for storage.

From starting block 602, flow diagram 600 proceeds to block 604, wheremaster control means 360 waits for a communication command from digitalsubsystem 390. In a preferred embodiment of the present invention, eachof the read-byte and write-byte commands includes an address for adesired memory location within slave digital subsystem 290 of slavestation 200. The write-byte command also includes a corresponding databyte. The address may comprise 2-32 binary bits for specifying thedesired memory location, as well-known in the semiconductor memory art.For the write command, digital subsystem 390 preferably provides eightdata bits for the data byte. It may be appreciated that error correctionbits may be included along with the eight data bits. Flow diagram 600then proceeds to block 606 where master control means 360 activates itsport 361 to prevent the oscillator signal at port 341 from being coupledto inductor means 310. This creates a resting duration in couplingmedium 110 between stations 200 and 300.

From block 606, flow diagram 600 proceeds to block 608 where controlmeans 360 couples a starting number of energy transitions to medium 110.A resting duration follows the starting number of energy transitions. Inone embodiment of the present invention, the starting number of energytransitions is on the order of 400 (corresponding to 200 energy pulsesand to 100 voltage cycles). The operation of master control means 360for coupling the starting number of energy transitions to medium 110 isdiscussed in greater detail below with reference to a flow diagram 630in FIG. 8. Flow diagram 630 is a flow diagram describing the stepsmaster control means 360 performs for coupling any specified number ofenergy transitions to coupling medium 110 and has general applicability.

From block 608, flow diagram 600 proceeds to block 610, where controlmeans 360 monitors its port 366 during this resting duration for aresponse from slave station 200 acknowledging receipt of the startingnumber of energy transitions. For this monitoring step, master controlmeans 360 de-activates its port 367 flow voltage) to enable transitionsensing means 370, waits a predetermined time for a response, and thenre-activates port 367 (high voltage) to disable transition sensing means370. If slave station 200 is powered up and initialized at this point,it will issue one or more energy transitions in this resting duration.If slave station 200 is not suitably powered and initialized, it willnot issue a response in this resting duration. Flow diagram 600 proceedsto block 612, where control means 360 determines whether slave station200 has issued a response during the resting duration. If no responsewas received, flow diagram 600 returns back to block 608, where astarting number of energy transitions is again coupled to medium 110. Ifa response has been received, flow diagram 600 proceeds to block 614.

At block 614, control means 360 determines if the command from digitalsubsystem 390 is a read-byte command. If it is a read command, flowdiagram 600 proceeds to block 620, where a byte of data is read fromslave station 200. The read-byte operation at block 620 is explained ingreater detail below with reference to a flow diagram 650 shown in FIGS.9A and 9B. If the command from digital substation 390 is not a read-bytecommand, flow diagram 600 proceeds to block 616. At this block, mastercontrol means 360 determines whether the command is a write-bytecommand. If so, flow diagram 600 proceeds to block 622 where a byte ofdata is written to slave station 200. The write-byte operation of block622 is explained in greater detail below with reference to a flowdiagram 700 shown in FIGS. 10A-10B. If the command is not a write-bytecommand, flow diagram 600 proceeds to block 618. Each of the operationsat blocks 620 and 622 also proceed to block 618 after their respectivesteps are completed.

At block 618, master control means 360 determines whether subsystem 390has issued a further communication command. If so, flow diagram 600proceeds to block 624 where the further command is obtained. If there isno further communication command, flow diagram 600 proceeds to block626, where master control means 360 terminates communications with slavestation 200. If a new command is received, flow diagram 600 returns to614 from block 624, where the nature of the command is determined. Flowdiagram 600 proceeds through blocks 614-624 as described above until nofurther communication commands are provided by digital substation 390.

It may be appreciated that the acknowledgment responses sent by slavestation 200 are not needed for communications to be enabled betweenstations 200 and 300 according to the present invention, but rather arefor providing a fault tolerant communication means, as in a furtherpreferred embodiment of the present invention. Thus, the operations ofblocks 610-612 are not necessary for carrying out the basic datacommunications according to the present invention, but rather arepreferred.

An exemplary flow diagram for coupling a selected number of energytransitions to coupling medium 110 is shown at 630 in FIG. 8. Flowdiagram 630 comprises blocks 632-642, starting at block 632, ending atblock 642, and proceeding sequentially through the blocks. At block 634,master control means 360 waits for a synchronization signal fromoscillator 340 indicating that a voltage cycle at oscillator output 341has substantially begun. The synchronization signal is provided at port362 of master control means 360. Upon receiving the synchronizationsignal, flow diagram 630 proceeds to block 636, where master controlmeans 360 deactivates its port 361. This allows the voltage cycles fromoscillator 340 to be coupled to driver stage 355, and on to inductormeans 310. Master control means 360 also counts the number of voltagecycles as indicated on its port 362 until the selected number of energytransitions is coupled to inductor means 310. The selected number may beany of the first, second, third, sixth, and seventh predeterminednumbers described above. At block 638, control means 360 waits for thenext zero current crossing indication at its port 363. Once receivingthe zero current crossing indication, flow diagram 630 proceeds to block638, where master control means 360 activates port 361 to create aresting duration. The resting duration is preferably on the order of onevoltage cycle, as indicated to master control means 360 on its port 362.By monitoring the zero crossing point at block 638 before creating theresting duration at block 640, control means 360 shuts down the signalto inductor means 310 to minimize any over-shoot or under-shoot effectsdue to the RLC circuit.

As described above, inductor means 310 and driver means 355 may besuitably characterized so as to determine the phase lag between thevoltage at oscillator output 341 and the current through inductor 310.Knowing this phase lag, the control means 360 may activate port 361 inblock 640 without requiring the monitoring of the zero current in block638. Rather, in this alternate embodiment, control means 360 deactivatesport 361 a predetermined time after the selected number of voltagecycles have been coupled, the predetermined time duration correspondingto the above-described phase lag.

Flow diagram 630 has general applicability and may be used to couple theabove-described starting number of energy transitions to coupling medium110. It may also be used to couple the first, second, third, sixth andseventh predetermined numbers to medium 110 as described below withreference to exemplary flow diagrams for the read-byte and write-byteoperations performed at blocks 620 and 622, respectively, in FIG. 7.

An exemplary flow diagram for generating a response for slave station200 is shown at 830 in FIG. 12. Flow diagram 830 comprises blocks832-848, starting at block 832, ending at block 848, and proceedingsequentially through the blocks. At block 834, slave control means 260de-activates its transition counter means from the signals at its ports261 and 262. This prevents the energy transitions which slave stationwill subsequently couple to medium 110 as its response from altering thevalue of the transition count. At block 836, slave control means 260de-activates the signal at its output port 264. This causes transistors278 and 279 to decouple storage capacitor 280 from the V_(DD) supplyprovided by power storage and regulation means 230, all shown in FIG.4B. At block 838, slave control means 260 activates the signal at itsoutput port 263, which causes transistors 276 and 277 to couplecapacitor 280 to inductor means 210 shown in FIG. 4B (or inductor means210' shown in FIG. 4C). Capacitor 280 resonates with inductor means 310to coupled one or more energy pulses and energy transitions to couplingmedium 110. At block 840, slave control means 260 waits a time durationin which at least one energy transition is coupled from slave station200. In a preferred embodiment of the present invention, this period isgreater than one-half a voltage cycle of master station 300. At block842, slave control means 260 de-activates the signal at its output port263, causing capacitor 280 to be isolated from inductor means 310, thusterminating the coupling of energy transitions to medium 110. At block844, slave control means 260 activates the signal on its output port 264to resume the charging of capacitor 280. At block 846, slave controlmeans 260 activates its transition counter means to the signals at itsports 261 and 262. Flow diagram 830 ends at block 848. It may beappreciated that the operations at blocks 834 and 846 may be eliminatedin those cases where the transition count is reset immediately followingthe issuance of a response.

Flow diagram 830 has general applicability and may be used to generatean acknowledgment response for slave station 200 as shown at block 810in FIG. 11. It may also be used to issues appropriate acknowledgmentresponses in the send data byte and receive data byte operations shownat blocks 818 and 820, respectively, in FIG. 11, as described below ingreater detail below with reference to exemplary flow diagrams for thesedata byte operations.

An exemplary flow diagram for the read-byte operation of block 620 isshown at a flow diagram 650 in FIGS. 9A-9B. Flow diagram 650 comprisesblocks 652-694, beginning at block 652 and ending at block 694. Inblocks 654 through 658, flow diagram 650 sends a read-byte command toslave station 200. In block 660 through 674, master control means 360sends the address to slave station 200. In block 676 through 692, mastercontrol means 360 reads a data byte from slave station 200. Each ofthese blocks is described in greater detail below.

From starting block 652, flow diagram 650 proceeds to block 654, wherecontrol means 360 couples the sixth predetermined number of energytransitions to coupling medium 110. Block 654 includes the steps of flowdiagram 630 shown in FIG. 8, with the selected number of energytransitions being equal to the sixth predetermined number. At the end ofthe steps of block 654, a resting duration in the energy transitions iscreated. The sixth predetermined number of transitions indicates toslave station 200 that master station 300 is requesting a byte of data.In response to receiving the sixth predetermined number of energytransitions, slave station 200 couples one or more energy transitions tomedium 110 during the subsequent resting duration, as an acknowledgementof receiving and understanding the read-byte command. However, there isa possibility that slave station 200 may not receive or understand theread-byte command due to electromagnetic interference or other reasons,and therefore does not respond. Flow diagram 650 proceeds to block 656,where master control means 360 monitors its port 366 for this responsefrom slave station 200. For this monitoring step, master control means360 de-activates its port 367 (low voltage) to enable transition sensingmeans 370, waits a predetermined time for a response, and thenre-activates port 367 (high voltage) to disable transition sensing means370.

From block 656, flow diagram 650 proceeds to block 658, where thedetermination is made whether slave station 200 has issued a response.If slave station has not issued a response, flow diagram 650 returnsback to block 654, where the sixth predetermined number of energytransitions is again coupled to medium 110. This provides faulttolerance for the communication system according to the presentinvention. If there is a response at block 658, flow diagram 650proceeds to block 660, where the process of sending the address to slavestation 200 begins.

At block 660, control means 360 obtains the first bit of the address andproceeds to block 662, where control means 360 determines whether thebit has a binary zero or a binary one value. If the bit is a binaryzero, flow diagram 650 proceeds to block 664, where master control means360 couples the first predetermined number of energy transitions tomedium 110. This block includes the steps of flow diagram 630 shown inFIG. 8, with the selected number of energy transitions being equal tothe first predetermined number. If the address bit is a binary one, flowdiagram 650 proceeds to block 666, where the second predetermined numberof energy transitions is coupled to medium 110. This block includes thesteps of flow diagram 630 shown in FIG. 8, with the selected number ofenergy transitions being equal to the second predetermined number. Atthe end of the steps of each block 664 and 666, a resting duration inthe energy transitions is created.

From block 664 and 666, flow diagram 650 proceeds to block 668, wheremaster control means 360 monitors its port 366 during the subsequentresting duration for a response from slave station 200 acknowledgingreceipt of either the first or second predetermined number of energytransitions. For this monitoring step, master control means 360de-activates its port 367 (low voltage), waits a predetermined time fora response, and the re-activates port 367 (high voltage). From block668, flow diagram 650 proceeds to block 670, where master control means360 determines whether a response from slave station 200 has beenreceived. If no response has been received, flow diagram 650 returnsback to block 654 to reissue the read-byte command. This provides faulttolerance for the communication system according to the presentinvention.

If a response is received, flow diagram 650 proceeds to block 672, wheremaster control means 360 determines whether the most recent bit sent isthe last bit in the address. If it is not the last bit, flow diagram 650proceeds to block 674, where the next address bit is obtained. Fromblock 674, flow diagram 650 returns back to block 662 to transmit thenext address bit to slave station 200 according to the operations ofblocks 662-670. If the most recent bit is the last address bit, flowdiagram 650 then proceeds to block 676, where the reception of therequested data byte from slave station 200 begins.

At block 676, the process of reading the first bit in the data byte fromslave station 200 begins. The process proceeds to block 678, where thethird predetermined number of energy transitions is coupled to medium110. This block includes the steps of flow diagram 630 shown in FIG. 8,with the selected number of energy transitions being equal to the thirdpredetermined number. Flow diagram 650 then proceeds to block 680, wheremaster control means 360 monitors its block 366 during the restingduration for a possible response back from slave station 200. For thismonitoring step, master control means 360 de-activates its port 367 (lowvoltage), waits a predetermined time for a response, and thenre-activates port 367 (high voltage). From block 680, flow diagram 650proceeds to block 682, where control means 360 determines whether aresponse from slave station 200 has been received. If no response hasbeen received, flow diagram 650 proceeds to block 684, where the bit isrecorded as a binary zero. However, if a response has been received,flow diagram 650 proceeds to block 686, where control means 360 recordsthe bit as a binary one.

Both blocks 684 and 686 then proceed to block 688, where control means360 determines whether the most recent bit is the last bit of therequested byte. If it is not the last bit, flow diagram 650 proceeds toblock 690, where the process for reading the next bit begins. From block690, flow diagram 650 returns back to block 678, where the thirdpredetermined number of energy transitions is coupled to medium 110. If,however, the most recent bit was the last bit in the byte, flow diagram650 proceeds to block 692, where the bits of the byte are sent tosubsystem 390. From block 692, flow diagram 650 proceeds to the endblock 694.

It may be appreciated that the acknowledgment responses sent by slavestation 200 are not needed for the communications between stations 200and 300 according to the present invention, but rather are for providinga fault tolerant communication means, as in a further preferredembodiment of the present invention. Thus, the operations of blocks656-658 and 668-670 are not necessary for carrying out datacommunications according to the present invention, but rather arepreferred.

An exemplary flow diagram for the write-byte operation of block 622shown in FIG. 7 is shown at 700 in FIGS. 10A and 10B. Flow diagram 700comprises blocks 702 through 742, starting at block 702 and ending atblock 742. At blocks 704 through 708, the write-byte command is issuedto slave station 200. In blocks 710 through 724, master control means360 sends the address of the byte to be written to slave station 200. Inblocks 726 through 740, control means 360 provides the data byte toslave station 200. The steps at each of these blocks is described ingreater detail below.

From starting block 702, flow diagram 700 proceeds to block 704, wherecontrol means 360 couples the seventh predetermined number of energytransitions to coupling medium 110. Block 704 includes the steps of flowdiagram 630 shown in FIG. 8, with the selected number of energytransitions being equal to the seventh predetermined number. At the endof the steps of block 704, a resting duration in the energy transitionsis created. The seventh predetermined number of transitions indicates toslave station 200 that master station 300 is providing a byte of data.

In response to receiving the seventh predetermined number of energytransitions, slave station 200 couples one or more energy transitions tomedium 110 during the subsequent resting duration, as an acknowledgementof receiving and understanding the write-byte command. However, there isa possibility that slave station 200 may not receive or understand thewrite-byte command due to electromagnetic interference or other reasons,and therefore does not respond. Flow diagram 700 proceeds to block 706,where master control means 360 monitors its port 366 for this responsefrom slave station 200. For this monitoring step, master control means360 de-activates its port 367 (low voltage), waits a predetermined timefor a response, and then re-activates port 367 (high voltage). Fromblock 706, flow diagram 700 proceeds to block 708, where thedetermination is made whether slave station 200 has issued a response.If slave station has not issued a response, flow diagram 700 returnsback to block 704, where the seventh predetermined number of energytransitions is again coupled to medium 110. This provides faulttolerance for the communication system according to the presentinvention. If there is a response at block 708, flow diagram 700proceeds to block 710, where the process of sending the address to slavestation 200 begins.

At block 710, control means 360 obtains the first bit of the address andproceeds to block 712, where control means 360 determines whether thebit has a binary zero or a binary one value. If the bit is a binaryzero, flow diagram 700 proceeds to block 714, where master control means360 couples the first predetermined number of energy transitions tomedium 110. This block includes the steps of flow diagram 630 shown inFIG. 8, with the selected number of energy transitions being equal tothe first predetermined number. If the address bit is a binary one, flowdiagram 700 proceeds to block 716, where the second predetermined numberof energy transitions is coupled to medium 110. This block includes thesteps of flow diagram 630 shown in FIG. 8, with the selected number ofenergy transitions being equal to the second predetermined number. Atthe end of the steps of each block 714 and 716, a resting duration inthe energy transitions is created.

From block 714 and 716, flow diagram 700 proceeds to block 718, wheremaster control means 360 monitors its port 366 during the subsequentresting duration for a response from slave station 200 acknowledgingreceipt of either the first or second predetermined number of energytransitions. For this monitoring step, master control means 360de-activates its port 367 (low voltage), waits a predetermined time fora response, and then re-activates port 367 (high voltage). From block718, flow diagram 700 proceeds to block 720, where master control means360 determines whether a response from slave station 200 has beenreceived. If no response has been received, flow diagram 700 returnsback to block 704 to reissue the write-byte command. This provides faulttolerance for the communication system according to the presentinvention.

If a response is received, flow diagram 700 proceeds to block 722, wheremaster control means 360 determines whether the most recent bit sent isthe last bit in the address. If it is not the last bit, flow diagram 700proceeds to block 724, where the next address bit is obtained. Fromblock 724, flow diagram 700 returns back to block 712 to transmit thenext address bit to slave station 200 according to the operations ofblock 712-720. If the most recent bit is the last address bit, flowdiagram 700 then proceeds to block 726, where the sending of the databyte to slave station 200 begins.

At block 726, the first bit of the data byte to be sent is obtained.Flow diagram 700 then proceeds to block 728, where control means 360determines whether the bit is a binary zero or binary one. If the bit isa binary zero, flow diagram 700 proceeds to block 730, where controlmeans 360 couples the first predetermined number of energy transitionsto coupling medium 110. This block includes the steps of flow diagram630 shown in FIG. 8, with the selected number of energy transitionsbeing equal to the first predetermined number. If the bit is a binaryone, flow diagram 700 proceeds to block 732, where the secondpredetermined number of energy transitions is coupled to medium 110.This block includes the steps of flow diagram 630 shown in FIG. 8, withthe selected number of energy transitions being equal to the secondpredetermined number. At the end of the steps of each block 730 and 732,a resting duration in the energy transitions is created.

From each of blocks 730 and 732, flow diagram 700 proceeds to block 734,where control means 360 monitors its port 366 during the subsequentresting duration for a response back from slave station 200acknowledging receipt of the data bit. For this monitoring step, mastercontrol means 360 de-activates its port 367 (low voltage), waits apredetermined time for a response, and then re-activates port 367 (highvoltage). Flow diagram 700 then proceeds to block 736, where controlmeans 360 determines whether slave station 200 has issued a response. Ifno response has been issued during the resting duration, flow diagram700 returns back to block 704, where control means 360 reissues thewrite-byte command to slave station 200. This provides fault tolerancefor the communication system according to the present invention. Ifslave station 200 issues a response, flow diagram 700 proceeds to block738, where master control means 360 determines if the most recent bitsent is the last bit in the data byte. If not, flow diagram 700 proceedsto block 740 where master control means 360 obtains the next bit in thedata byte. From block 740, flow diagram 700 returns back to block 728 totransmit the next bit to slave station 200. If the most recent bit isthe last bit, flow diagram 700 proceeds to block 742 where it ends.

It may be appreciated that the acknowledgment responses sent by slavestation 200 are not needed for the communications between stations 200and 300 according to the present invention, but rather are for providinga fault tolerant communication means, as in a further preferredembodiment of the present invention. Thus, the operations of blocks706-708,718-720, and 734-736 are not necessary for carrying out datacommunications according to the present invention, but rather arepreferred.

A flow diagram of the operation of an exemplary slave control means 260for master station 300 according to the present invention is shown at800 in FIG. 11. Flow diagram 800 comprises blocks 802-822, beginning atblock 802 and ending at block 822. In blocks 804 through 810, slavecontrol means 260 synchronizes communications with master station 300.In blocks 812-822, slave control means 260 interprets the communicationcommand from master station 300, executes the communication command, andthen checks for a further communication command.

From starting block 802, flow diagram 800 proceeds to block 804 whereslave control means 260 detects the application of power at its port244, shown in FIG. 4B. From block 804, flow diagram 800 proceeds toblock 806, where slave control means 260 sets its energy transitioncount to zero. As indicated above, a digital counter means, as wellknown in the digital circuit arts, may be used for holding thetransition count. From block 806, flow diagram 800 proceeds to block808, where slave control means 260 monitors its port 262 for anindication of an absent energy transition, or resting duration, asprovided by master station 300 at the end of block 608 shown in FIG. 7.Once a resting duration is detected, flow diagram 800 proceeds to block810, where slave control means 260 issues a response for slave station200. This response is detected by master control means 360 at blocks610-612 of flow diagram 600 shown in FIG. 7. The operation of slavecontrol means 260 for issuing a response by coupling a number of energytransitions to medium 110 is described below in greater detail withreference to a flow diagram 830 shown in FIG. 12.

From block 810, flow diagram 800 proceeds to block 812, where slavecontrol means 260 counts the number of transitions indicated on itsinput port 261 until a resting duration is indicated on its input port262. Flow diagram 800 proceeds to block 814, where slave control means260 determines whether the number of counted transitions indicates thatmaster station 300 is issuing a read-byte command (the sixthpredetermined number of energy transitions). If so, flow diagram 800proceeds to block 818 where a send-byte operation is performed. Thesend-byte operation at block 818 is explained in greater detail belowwith reference to a flow diagram 850 shown in FIGS. 13A and 13B. If thecommand from master station 300 is not a read-byte command, flow diagram800 proceeds to block 816. At this block, slave control means 260determines whether the number of counted transitions indicates thatmaster station 300 is issuing a write-byte command (the seventhpredetermined number of energy transitions). If so, flow diagram 800proceeds to block 820 where byte of data is received from master station300. The receive-byte operation of block 820 is explained in greaterdetail below with reference to a flow diagram 900 shown in FIGS.14A-14B. If the command is not a write-byte command, flow diagram 800proceeds to block 822. Each of the operations at blocks 818 and 820 alsoproceed to block 822 after their respective steps are completed. Atblock 822, slave control means 260 sets its transition count to zero.Flow diagram 800 then returns back to block 812 to count transitions andthereby be enabled to interpret the next command from master station300.

An exemplary flow diagram for the send-byte operation of block 818 isshown at a flow diagram 850 in FIGS. 13A-13B. Flow diagram 850 comprisesblocks 852-892, beginning at block 852 and ending at either of blocks865 or 892, depending upon transmission conditions. From starting block852, flow diagram 850 proceeds to block 854, where slave control means260 issues a response to acknowledge receipt of the read-byte command.This block includes the steps of flow diagram 830 shown in FIG. 12. Thisresponse is detected by master control means 360 at blocks 656-658 offlow diagram 650 shown in FIG. 9A. From block 854, flow diagram 850proceeds to block 856, where slave control means 260 resets itstransition count. From block 856, flow diagram 850 proceeds to block858. In blocks 858 through 875, slave control means 260 receives anaddress from master station 300. In block 876 through 890, slave controlmeans 260 sends a data byte to master station 300. Each of blocks858-890 is described in greater detail below.

At block 858, slave control means 260 begins the process of receivingthe address for the byte of data which master station 300 is requesting.In a preferred embodiment, the process comprises receiving sets of firstand second predetermined numbers of energy transitions, issuingacknowledgement responses, and outputting corresponding address bits todigital subsystem 290. At block 858, reception of the first address bitbegins. Flow diagram 850 proceeds to block 860, where slave controlmeans 260 counts the number of transitions indicated on its input port261 until a resting duration is indicated on its input port 262. Fromblock 860, flow diagram 850 proceeds to block 862 where slave controlmeans 260 determines whether the number of counted transitions indicatesa binary zero (first predetermined number). If so, flow diagram 850proceeds to block 866, where slave control means 260 sends a binary zeroaddress bit to digital subsystem 290 or, in an alternative embodiment,records a binary zero address bit for later transmission to subsystem290 after the last address bit has been received. If the number oftransitions does not indicate a binary zero address bit, flow diagram850 proceeds to block 864, where slave control means 260 determineswhether the number of counted transitions indicates a binary one (secondpredetermined number). If so, flow diagram 850 proceeds to block 868,where slave control means 260 sends a binary one address bit to digitalsubsystem 290 or, in an alternative embodiment, records a binary zeroaddress bit for later transmission to subsystem 290 after the lastaddress bit has been received. If the number of transitions does notindicate a binary zero address bit, flow diagram 850 proceeds to block865 where the send-byte operation is terminated. This may occur ifelectromagnetic interference has altered the number of energytransitions coupled to slave station 200 by master station 300. In thiscase, slave control means proceeds to block 822 (from block 818) of flowdiagram 800 shown in FIG. 11. Master control means 360 detects thistransmission error condition at block 670 of flow diagram 650 (shown inFIG. 9A) because slave station 200 does not issue an acknowledgementresponse.

From each of blocks 866 and 868, flow diagram 850 proceeds to block 870,where slave control means 260 issues a response acknowledging receipt ofthe address bit. This block includes the steps of flow diagram 830 shownin FIG. 12. This response is detected by master control means 360 atblocks 668-670 of flow diagram 650 shown in FIG. 9A. From block 870,flow diagram 850 proceeds to block 872, where slave control means 260resets its transition count. Flow diagram 850 then proceeds to block874, where slave control means 260 determines whether the most recentaddress bit sent by master station 300 is the last bit in the address.If it is not the last bit, flow diagram 850 proceeds to block 875, wherecontrol means 260 prepares to receive the next address bit. From block875, flow diagram 850 returns back to block 860 to receive the nextaddress bit according to the operations of blocks 860-872. If the mostrecent bit is the last address bit, flow diagram 850 then proceeds toblock 876, where slave control means 860 receives a data byte fromdigital subsystem 290 which corresponds to the received address.

From block 876, flow diagram 850 proceeds to block 878, where slavecontrol means 260 gets the first bit of the data byte and begins theprocess of sending the first data bit to master station 300. From block878, flow diagram 850 proceeds to block 880, where slave control means260 counts transitions until a resting duration occurs. In a preferredembodiment of the present invention, the number of counted transitionsis equal to the third predetermined number. From block 880, flow diagram850 proceeds to block 882, where slave control means determines whetherthe current bit being sent represents a binary one or a binary zerovalue. If the current bit represents a binary one value, flow diagram850 proceeds to block 884, where slave control means issues a responsecomprising the coupling of one or more energy transitions to couplingmedium 110. This block includes the steps of flow diagram 830 shown inFIG. 12. From block 884, flow diagram 850 proceeds to block 886, whereslave control means 260 resets its transition count. If the current bitrepresents a binary zero value, flow diagram 850 proceeds from block 882to block 886 to reset the transition count without issuing a response.Master control means 360 detects whether a response during this restingduration occurs and records a binary one value if one or moretransitions occur and a binary zero value if no transitions occur (cf.blocks 680-686 of flow diagram 650 shown in FIGS. 9A-9B). In this way, abinary digit is sent to master station 300.

From block 886, flow diagram 850 proceeds to block 888, where slavecontrol means 260 determines whether the most recent bit sent was thelast bit in the data byte. If it is not the last bit, flow diagram 850proceeds to block 890, where the next address bit is obtained. Fromblock 890, flow diagram 850 returns back to block 880 to transmit thenext data bit to master station 300 according to the operations ofblocks 880-886. If the most recent bit is the last data bit, flowdiagram 850 proceeds to block 892, where the send byte operation ends.The operation of slave control means 260 returns to block 822 (fromblock 818) of flow diagram 800 shown in FIG. 11.

An exemplary flow diagram for the receive-byte operation of block 820 isshown at a flow diagram 900 in FIGS. 14A-14B. Flow diagram 900 comprisesblocks 902-946, beginning at block 902 and ending at either of blocks915, 935, or 946, depending upon transmission conditions. From startingblock 902, flow diagram 900 proceeds to block 904, where slave controlmeans 260 issues a response to acknowledge receipt of the write-bytecommand. This block includes the steps of flow diagram 830 shown in FIG.12. This response is detected by master control means 360 at block 706of flow diagram 700 shown in FIG. 10A. From block 904, flow diagram 900proceeds to block 906, where slave control means 260 resets itstransition count. From block 906, flow diagram 900 proceeds to block908. In blocks 908 through 925, slave control means 260 receives anaddress from master station 300. In block 926 through 945, slave controlmeans 260 receives a data byte from master station 300. Each of blocks908-945 is described in greater detail below.

At block 908, slave control means 260 begins the process of receivingthe address of the byte of data which master station 300 is sending. Ina preferred embodiment, the process comprises receiving sets of firstand second predetermined numbers of energy transitions, issuingacknowledgement responses, and outputting corresponding address bits todigital subsystem 290. At block 908, reception of the first address bitbegins. Flow diagram 900 proceeds to block 910, where slave controlmeans 260 counts the number of transitions indicated on its input port261 until a resting duration is indicated on its input port 262. Fromblock 910, flow diagram 900 proceeds to block 912 where slave controlmeans 260 determines whether the number of counted transitions indicatesa binary zero (first predetermined number). If so, flow diagram 900proceeds to block 916, where slave control means 260 sends a binary zeroaddress bit to digital subsystem 290 or, in an alternative embodiment,records a binary zero address bit for later transmission to subsystem290 after the last address bit has been received. If the number oftransitions does not indicate a binary zero address bit, flow diagram900 proceeds to block 914, where slave control means 260 determineswhether the number of counted transitions indicates a binary one (secondpredetermined number). If so, flow diagram 900 proceeds to block 918,where slave control means 260 sends a binary one address bit to digitalsubsystem 290 or, in an alternative embodiment, records a binary zeroaddress bit for later transmission to subsystem 290 after the lastaddress bit has been received.

If the number of transitions does not indicate a binary zero addressbit, flow diagram 900 proceeds to block 915 where the receive-byteoperation is terminated. This may occur if electromagnetic interferencehas altered the number of energy transitions coupled to slave station200 by master station 300. In this case, slave control means proceeds toblock 822 (from block 820) of flow diagram 800 shown in FIG. 11. Mastercontrol means 360 detects this transmission error condition at block 720of flow diagram 700 (shown in FIG. 10A) because slave station 200 doesnot issue an acknowledgement response.

From each of block 916 and 918, flow diagram 900 proceeds to block 920,where slave control means 260 issues a response acknowledging receipt ofthe address bit. This block includes the steps of flow diagram 830 shownin FIG. 12. This response is detected by master control means 360 atblock 718-720 of flow diagram 700 shown in FIG. 10A). From block 920,flow diagram 900 proceeds to block 922, where slave control means 260resets its transition count. Flow diagram 900 then proceeds to block924, where slave control means 260 determines whether the most recentaddress bit sent by master station 300 is the last bit in the address.If it is not the last bit, flow diagram 900 proceeds to block 925, wherecontrol means 260 prepares to receive the next address bit. From block925, flow diagram 900 returns back to block 910 to receive the nextaddress bit according to the operations of block 910-922. If the mostrecent bit is the last address bit, flow diagram 900 then proceeds toblock 928.

At block 928, slave control means 260 prepares to receive the bits ofthe data byte being sent by master station 300. In a preferredembodiment, the process comprises receiving sets of first and secondpredetermined numbers of energy transitions, issuing knowledgementresponses, and outputting corresponding data bits to digital subsystem290. At block 928, reception of the first data bit begins. Flow diagram900 proceeds to block 930, where slave control means 260 counts thenumber of transitions indicated on its input port 261 until a restingduration is indicated on its input port 262. From block 930, flowdiagram 900 proceeds to block 932 where slave control means 260determines whether the number of counted transitions indicates a binaryzero (first predetermined number). If so, flow diagram 900 proceeds toblock 936, where slave control means 260 sends a binary zero data bit todigital subsystem 290 or, in an alternative embodiment, records a binaryzero data bit for later transmission to subsystem 290 after the lastdata bit has been received. If the number of transitions does notindicate a binary zero data bit, flow diagram 900 proceeds to block 934,where slave control means 260 determines whether the number of countedtransitions indicates a binary one (second predetermined number). If so,flow diagram 900 proceeds to block 938, where slave control means 260sends a binary one data bit to digital subsystem 290 or, in analternative embodiment, records a binary zero data bit for latertransmission to subsystem 290 after the last data bit has been received.

If the number of transitions does not indicate a binary zero data bit,flow diagram 900 proceeds to block 935 where the receive-byte operationis terminated. This may occur if electromagnetic interference hasaltered the number of energy transitions coupled to slave station 260 bymaster station 300. In this case, slave control means proceeds to block822 (from block 820) of flow diagram 800 shown in FIG. 11. Mastercontrol means 360 detects this transmission error condition at block 736of flow diagram 700 (shown in FIG. 10B) because slave station 200 doesnot issue an acknowledgement response.

From each of blocks 936 and 938, flow diagram 900 proceeds to block 940,where slave control means 260 issues a response acknowledging receipt ofthe data bit. This block includes the steps of flow diagram 830 shown inFIG. 12. (This response is detected by master control means 360 atblocks 734-736 of flow diagram 700 shown in FIG. 10B). From block 940,flow diagram 900 proceeds to block 942, where slave control means 260resets its transition count. Flow diagram 900 then proceeds to block944, where slave control means 260 determines whether the most recentdata bit sent by master station 300 is the last bit in the data byte. Ifit is not the last bit, flow diagram 900 proceeds to block 945, wherecontrol means 260 prepares to receive the next data bit. From block 945,flow diagram 900 returns back to block 930 to receive the next data bitaccording to the operations of blocks 930-942. If the most recent bit isthe last data bit, flow diagram 900 then proceeds to block 946, whereslave control proceeds to block 946, where the receive byte operationends. The operation of slave control means 260 returns to block 822(from block 820) of flow diagram 800 shown in FIG. 11.

Alternate embodiments for coil form 315, inductor means 310, andinductor means 320 are now described with reference to FIGS. 15A and15B. Shown in FIG. 15A are an alternate coil form 315A, a power inductormeans 310A, and a data receiving inductor means 320A. Coil form 315Acorresponds in function to coil form 315 shown in FIG. 3, and inductormeans 310A and 320A correspond respectively to inductor means 310 and320, shown in FIG. 3. Also shown in FIG. 15A are coupling medium 110,slave station 200, including substrate 205. Coil form 315A comprises abody of ferromagnetic material shaped in the form of a "C". Inductormeans 310A and 320A are wrapped around the midsection of coil form 315A,as shown in FIG. 15A. Between the ends of coil form 315A an air gap isformed, which serves for receiving substrate 205, as shown in FIG. 15A.Electromagnetic coupling medium 110 is disposed in the air gap, asindicated.

Shown in FIG. 15B is an alternative inductor means 310B on a secondalternate coil form 315B. Inductor means 310B corresponds in function toinductor means 310 shown in FIG. 3. Also shown in FIG. 15B are slavestation 200, including substrate 205, and electromagnetic couplingmedium 110. Coil form 315B comprises two bodies of ferromagneticmaterial, each preferably in the form of a cylinder. The two bodies ofcoil form 315B are disposed opposite one another with an air gap formedbetween confronting surfaces thereof. Electromagnetic coupling medium110 is disposed in this air gap, as shown in FIG. 15B. As with theprevious embodiment of the coil form according to the present invention,the air gap is for receiving substrate 205.

Inductor means 310B comprises a first plurality of windings disposedabout the outer cylindrical surface of the first body of coil form 315B,and a second plurality of windings disposed about the outer cylindricalsurface of the second body of coil form 315B. The two sets of windingsfor inductor means 310B are coupled together to form two (2) windingselectrically coupled in parallel on both sides of coil form 315B. Thesewindings are coupled such that the magnetomotive forces generated byeach winding add constructively in the air gap between the two bodies.Inductor means 310B comprises a first terminal 311B, which is coupled toa first terminal of each of the windings, and a second terminal 312B,which is coupled to a second terminal of each of the windings. A datareceiving inductor means, such as means 320, may be disposed about theouter cylindrical surface of either body of 315B.

Inductor means 310B and coil form 315B have the advantage, with respectto inductor means 310 and coil form 315 shown in FIG. 3, of providingbetter electromagnetic coupling to slave station 200 from both the topand bottom surfaces of substrate 205. With respect to coil form 315A andinductor means 310A shown in FIG. 15A, inductor means 310B and coil form315B have significantly less core losses due to the close placement ofinductor means 310B to coupling medium 110. As known in the art, manyferromagnetic materials have significant core losses due to eddycurrents. Thus, for coupling the maximum amount of power from inductormeans 310 to slave station 200, inductor means 310B and coil form 315Bare preferred over inductor means 310A and coil form 315A, and overinductor means 310 and coil form 315, shown in FIG. 3.

Having described exemplary communication system 100, master station 300,and slave station 200, further embodiments thereof are now described. Inone further embodiment of communication system 100, master station 300and slave station 200 are configured as a key entry system where slavestation 200 serves to identify the holder of the key (e.g., a humanuser) and master station 300 selectively allows entry of key holder intoa desired area, such as a house, business, warehouse, or classifiedsecurity area. In this embodiment, digital subsystem 290 of slavestation 200 includes an identifier having a plurality of non-volatiledata digits, and digital subsystem 390 of master station 300 includesone or more commands, e.g., one or more read-byte commands, forobtaining the identifier from slave station 200. Additionally, digitalsubsystem 390 includes means for confirming, or authenticating, theidentifier of the key holder, such as, for example, a non-volatilememory table of all allowable, i.e., predetermined, identifier values.Also, digital subsystem 390 further includes means responsive to theconfirmation of the identifier for controlling access to the desiredarea, such as, for example, means for generating a digital signal whichdirects a locking mechanism to open. An advantage of the presentinvention is that the identifier of the key holder (slave station 200)may be readily changed without having to replace the key.

In this embodiment of the present invention, as well as otherappropriate embodiments, slave station 200 may be provided on a badge, aring, a key, a coin, or a token.

In another embodiment of communication system 100, master station 300and slave station 200 are configured as a credit-card authorizationsystem where slave station 200 serves to provide the credit accountinformation of a card user to master station 300 and master station 300evaluates the user's account information in view of a desired purchaseand selectively authorizes the purchase depending upon the amount andcredit account information. In this embodiment, digital subsystem 290 ofslave station 200 includes an account number identifier having aplurality of non-volatile data digits and, optionally, an accountexpiration date having a plurality of data digits. Additionally, digitalsubsystem 390 of master station 300 includes one or more commands, e.g.,one or more read-byte commands, for obtaining the account number, andoptionally expiration date, from slave station 200. Additionally,digital subsystem 390 includes means for confirming, or authenticating,the credit of the card user against the purchase amount, such as forexample by transmitting the account number and purchase amount to acentral credit agency for approval. An advantage of this system of thepresent invention is that a personalized identification number may beincluded to prevent unauthorized persons from using the card. Anotheradvantage is that a credit balance may be included within digitalsubsystem 290 and updated as purchases are made. This would allow theuse of the credit card without having to immediately transmit theaccount information and purchase amount to the central credit agency forapproval. As purchases are made, the credit balance is updated (i.e.,reduced). As such, the transaction time for a purchase may be reduced.Periodically, the balance on the card and the balance at the centralcredit agency may be reconciled.

In another embodiment of communication system 100, master station 300and slave station 200 are configured as a electronic coin or tokensystem where slave station 200 carries an adjustable monetary value forthe card user to be used to electronically pay for services, such asphotocopying or transportation fares. Master station 300 reads thecurrent monetary value and, when the purchase amount is less than thecurrent monetary value, authorizes the purchase and adjusts the monetaryvalue to reflect the purchase. In this embodiment, digital subsystem 290of slave station 200 includes a plurality of non-volatile data digitsfor storing the monetary value. Additionally, digital subsystem 390 ofmaster station 300 preferably includes one or more commands, e.g., oneor more read-byte commands, for obtaining the monetary value and forupdating the value after a purchase is made (i.e., providing a revisedmonetary value to slave station 200). An advantage of this system of thepresent invention is that monetary transactions could be greatlysimplified since the need for providing exact change and the changing oflarge denomination bill would not be necessary. Another advantage isthat a personalized identification number may be included to preventunauthorized persons from using the money indicated by the electroniccoin.

In another embodiment of communication system 100, master station 300and slave station 200 are configured as an electronic labeling systemwhere slave station 200 serves to provide information for an object(e.g., a shipping container or a human) to which it is affixed andmaster station 300 accesses the information and, optionally updates oramends the information given certain events. In this embodiment, digitalsubsystem 290 of slave station 200 preferably includes a plurality ofnon-volatile data digits for storing the information and digitalsubsystem 390 of master station 300 includes one or more commands, e.g.,one or more read-byte commands, for obtaining the information from slavestation 200. In the case where the object is a shipping container or thelike, the information may include such things as the origin anddestination of the container, the date shipped, and the contents. In thecase where the object is a human, the information may include themedical history, medical ailments, and allergic reactions of the human.An advantage of this system of the present invention is that a greatdeal of information may be provided within slave station 200. A furtheradvantage is that this information can be configured such that it isaccessible only to authorized persons.

While the present invention has been particularly described with respectto the illustrated embodiments, it will be appreciated that variousalterations, modifications and adaptations may be made based on thepresent disclosure, and are intended to be within the scope of thepresent invention. While the invention has been described in connectionwith what is presently considered to be the most practical and preferredembodiments, it is to be understood that the present invention is notlimited to the disclosed embodiment(s) but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the scope of the appended claims.

What is claimed is:
 1. A system for data transmission between a masterstation and a slave station in which an electromagnetic coupling mediumis formed between the master station and the slave station, theelectromagnetic coupling medium being capable of communicating databi-directionally between the master station and the slave station in theform of electromagnetic energy transitions, said system comprising:meansin said master station for transmitting a first digital value to saidslave station, including means for causing a first predetermined numberof energy transitions to be coupled to said medium followed by a firstresting duration in which substantially no energy transitions arecoupled to said medium by said master station, said energy transitionsbeing coupled through said medium in the form of energy pulses, eachsaid energy pulse having a first energy level, a second energy level,and energy transitions between said first and second energy levels;means in said master station for transmitting a second digital value tosaid slave station, including means for causing a second predeterminednumber of energy transitions to be coupled to said medium followed by asecond resting duration in which substantially no energy transitions arecoupled to said medium by said master station; means in said slavestation for detecting from said medium said first predetermined numberof energy transitions followed by said first resting duration and foroutputting a signal representative of said first digital value inresponse thereto, and for detecting said second predetermined number ofenergy transitions followed by said second resting duration and foroutputting a signal representative of said second digital value inresponse thereto; and means in said slave station for powering saidslave station from the energy pulses coupled to it by said masterstation through said electromagnetic coupling medium.
 2. The system ofclaim 1 further comprising:means in said master station for initiating aread operation from said slave station, including means for causing athird predetermined number of energy transitions to be coupled to saidmedium followed by a third resting duration in which substantially noenergy transitions are coupled to said medium by said master station;means in said slave station for detecting from said medium said thirdpredetermined number of energy transitions followed by said thirdresting duration and for outputting a read command signal in responsethereto, means in said slave station responsive to said read commandsignal for transmitting a binary zero value to said master station,including means for causing a fourth predetermined number of energytransitions to be coupled to said medium by said slave station duringsaid third resting duration; means in said slave station responsive tosaid read command signal for transmitting a binary one value to saidmaster station, including means for causing a fifth predetermined numberof energy transitions to be coupled to said medium by said slave stationduring said third resting duration, said fifth predetermined numberbeing different from said fourth predetermined number; means in saidmaster station for detecting from said medium said fourth predeterminednumber of energy transitions during said third resting duration and foroutputting a signal representative of said binary zero value in responsethereto; and means in said master station for detecting from said mediumsaid fifth predetermined number of energy transitions during said thirdresting duration and for outputting a signal representative of saidbinary one value in response thereto.
 3. The system of claim 2 whereinsaid third predetermined number is different from said firstpredetermined number and is different from said second predeterminednumber.
 4. The system of claim 2 wherein said fourth predeterminednumber of energy transitions used for transmitting said binary zerovalue is zero, and wherein said fifth predetermined number of energytransitions used for transmitting said binary one value is at least one.5. The system of claim 1 wherein said first digital value represents abinary zero of a binary digit and said second value represent a binaryone of said binary digit.
 6. The system of claim 1 wherein saidelectromagnetic energy coupling medium conveys the energy transitionssubstantially in the form of magnetomotive force, energy.
 7. The systemof claim 1 wherein said first energy level of each said energy pulse issubstantially zero and wherein said second energy level of each saidenergy pulse is a non-zero energy value.
 8. A system for datatransmission between a master station and a slave station in which anelectromagnetic coupling medium is formed between the master station andthe slave station, the electromagnetic coupling medium being capable ofcommunicating data hi-directionally between the master station and theslave station in the form of electromagnetic energy transitions, saidsystem comprising:means in said master station for initiating a readoperation from said slave station, including means for causing a firstpredetermined number of energy transitions to be coupled to said mediumfollowed by a first resting duration in which substantially no energytransitions are coupled to said medium by said master station; means insaid slave station for detecting from said medium said firstpredetermined number of energy transitions followed by said firstresting duration and for outputting a read command signal in responsethereto, means in said slave station responsive to said read commandsignal for transmitting a binary zero value to said master station,including means for causing a second predetermined number of energytransitions to be coupled to said medium by said slave station duringsaid first resting duration; means in said slave station responsive tosaid read command signal for transmitting a binary one value to saidmaster station, including means for causing a third predetermined numberof energy transitions to be coupled to said medium by said slave stationduring said first resting duration, said third predetermined numberbeing different from said second predetermined number; means in saidmaster station for detecting from said medium said second predeterminednumber of energy transitions during said first resting duration and foroutputting a signal representative of said binary zero value in responsethereto; and means in said master station for detecting from said mediumsaid third predetermined number of energy transitions during said firstresting duration and for outputting a signal representative of saidbinary one value in response thereto.